I needed to edit an animated gif on Mac OS X today…tried Acorn, but it doesn’t seem to support them. Tried Gimp, but it was unusable…could be user error, but every tool I selected would not stay selected and I couldn’t paste between documents.
Then I downloaded Pixen and despite it crashing the first time I tried saving the GIF, it worked great. And it’s free.
One note: if you use multiple layers in the frames, you need to merge them into one layer for the output to be correct.