Some guy with a name that I can't pronouncedecided to compare features in Firefox extensions with Opera default options and widgets. Then he did it again. Then some other guy with a name I also cannot pronounce did it for the 150 most popular Firefox extnensions. Northern Europeans have nothing but time on their hands.
Also, this thing brings you closer to GDrive/Gmail as a hard drive/virtual computer/etc. Again, I don't advocate using your e-mail account as a hard drive per se (especially if GDrive comes to fruition), but it's worth bearing in mind for those who are already storing a million files with Gmail. Use with caution, don't blame me if it doesn't work like you want. See also the Gmail Space Firefox extension, and Gmail Skins for some features that are purely aesthetic but some that are also functional.