Daves on it.
They can be huge in file size.. but this one for instance is a 140 by 130 pixel size of about 5 or 6 'slices' (as they are called in ImageReady), which came to about 54 KB. (The Avatar limits are 150 square max, and 58.7 KB).
When you make a layered GIF, then go to (take it into) Image Ready, then click on File/Optomise and save as a GIF, Animated, regular file order for animation.
I had done one if the LearFan years ago by taking screenshots of it at angles in Gmax (I made a Gmax scene with the plane rotating via the slider, taking screenshots at certain angles through the rotation).
I then took all screenshots, put them in a stack in PS, all in order, then cropped it for the right amount of edge size, then export (jump) to ImageReady, then use animation options (blend) and then Optomize. Oops.. and resize.. You can make several, one huge, one medium, then one super small for Avatars..
Bill