Introduction

As nearly everybody knows now, deviantART have released Gallery v2.
I saw lot of questions, of suggestions of features already existing, and so on, so I thought I could share the result of my experiments in this field.
A quick search didn't show news on this topic, and not yet items in the Help & FAQ section.
EDIT: I submit to Fin > Technology (seems appropriate...) because I have no right to submit in deviantART, Inc. > Tech & Features or Help & FAQ.

Disclaimer: I tested mostly with Firefox 2 on Windows XP SP2, and of course with my gallery. Some people have larger galleries and experienced other problems.
Note: when reporting an issue with dA, it is always a good idea to indicate which browser you use, and which OS too, as results (and issues!) can differ greatly from one browser to another, despite the attempts of dA programmers to handle the differences.
Notice to Safari users: I saw that previous version of Safari, the browser made by Apple, suffered from bad JavaScript implementation, hindering advanced features like Gallery Stats and Gallery Folders. It seems that the latest version corrects a number of these issues, so you should upgrade if you can.
In general, before reporting an issue, check the Gallery v2 - Known Issues sticky thread in the Status forum.

What is it?

If you went somebody else's gallery, you must have seen a change of look. We have three items at the top of the page: Featured (simple text) Everything (link) and Categories (with a drop down arrow).

By default, you see the Featured page, which is close of the old Gallery view if the deviant didn't change anything.
If the deviant has played with the feature, you probably see a set of folders on the left part of the page, and the Featured page might show only a small subset of the deviations of this deviant, those he/she chose to highlight.

To see all the deviations of this deviant, you can click on the Everything link. It is even closer of the old Gallery view, with chronological order (in Newest mode) or by popularity, category and date display, and the much requested link to the Daily Deviations of this deviant, if it has received any.
One of the biggest difference is that scraps are shown too. Some people love this ("Hey, that's Everything!", "Scraps are under-appreciated"), lot of other people hate that ("Scraps are made to be hidden, or cleanly separated from finished work").

If you click on the Category link, you will see a change from the old one: only the categories actually used by the deviant are shown. A big improvement!

Now, the folders: click on one, you will see the deviations the deviant has put there, in the order it chose: the first three deviations are used as thumbnail of the folder. You can go back to the gallery by using the arrow on top-left corner of the page.

Nice no? Now you want to organize your own gallery, surely.

How to use?

Create folders

Go to your own gallery. You have the same view, except there is a blue button labeled Edit on the right of the Featured/Everything/Categories items.
Tempting, eh? Click on it!

You get a special view, with a dark band on top, showing Editing on left, and a Done button on right. Every deviation gets, below it, a blue button with a down arrow on it, and the left side of the window has a + blue button with a New Folder legend below.
Click on the + button. It shifts down, showing a dark area with a crossed red button on top-right and an edit area filled with "Devious Folder".
If you look at the dark status bar, you can see the messages Auto-saving changes... then Auto-saved. This means that every change you made is transmitted to dA servers.

Type a folder name, validate with Enter (or Return). You can use letters, numbers, spaces, and a limited set of characters which seems to be - . ? ' $ " _ \ If you type another character, the change is rejected and the title reverts to the old one. A bit annoying...

Populate folders

You can start putting deviations in this folder. There are two ways:

• Click on a deviation, holding down the mouse button. Move the mouse, you drag the deviation. Release the button when it is over the folder, you drop it there. While I test what I write, I see that the first deviation dropped in a new folder is "rejected". The second time I drag it there, it works. A quirk that might disappear later.


• Click on the blue button with arrow below a deviation. You can see a menu:

  
  Remove from "Featured"
  Put in "Folder name"

  
  where "Folder name" is actually the one you typed. If you select the second item, it will be added to the folder. And the menu becomes:

  
  Remove from "Featured"
  Remove from "Folder name"

A cool, often overlooked feature, is that you can put a deviation in several folders. Create another folder: you can see Put in "New folder" item in the drop down menu (where "New folder" is actually the name you typed), and you can also drag'n'drop the same deviation in the new folder. Very handy!

As you have seen, you can remove deviations from the Featured folder. Actually, it is just another folder, which by default hold all your non-scrap deviations. You can trim it down by selecting this option for the deviations you think are weaker, leaving only those you want to be remarked.
What if you change your mind? No problem, you can find back your deviation in the Everything view, and select Put in "Featured" there.

Note that if you scrolled down to the bottom of your page, the folders are out of view. You can still use drag'n'drop: move the mouse to the top (or bottom) limits of the window, and it will automatically scroll until the target position is in view. It might be more practical/faster, though, to use the drop down menu in this case.

Delete folders

If you click on the red crossed disk, you will delete the folder. If it is not empty, a confirmation is asked. The deviations in the folder are not deleted, of course! They are just no longer classified in this folder.

Re-order deviations

If you are in a folder ("Featured" or one you created), you can drag a deviation inside the page: as long as you hold down the mouse button, a big black vertical line is displayed between the deviations. It shows the position the deviation you drag will take if you release the button. To cancel the move, drag it back to its place, or just move it outside of the list of deviations. Here again, if you move near the window's limits, the display will auto-scroll.

Describe folders

If you go in a folder in Edit mode (you cannot enter in edit mode while in a folder, you have to be in the main gallery view to go in this mode), you can see a blue options button. Click on it: you see a kind of dialog with two edit fields (Name and Text) and three buttons: OK, Cancel and Delete.
The name field allows you to rename the folder. Amusing fact: you can type here characters rejected in the main gallery, namely , : + Other characters cause an error, displaying a dialog telling that the change cannot be saved, asking if you want to try again. Click No, it won't work anyway.
The Text field allows you to type a multi-line description of the folder: it will be displayed on top of the folder when a deviant visits it.
OK validates the change, Cancel drops them, Delete allows to delete the folder, beware!

Conclusion

When you are done playing with your gallery, click the... Done button! Since every change is auto-saved, it is not really necessary: if you go elsewhere, you just go out of edit mode.

This new feature made lot of enthusiasm and some unavoidable complains. I think it might still evolve, it is young. But it will definitively change the way deviants browse deviantART!