One of the reasons I prefer Epiphany over Firefox
is was that different web sites had different icons, which made it easier to pick them out in superswitcher or the window list (aka taskbar). Another reason is that it didn’t stick “- Mozilla Firefox” at the end of everything, which again makes things easier to pick out. Here’s a thousand words:
This little issue seems somewhat apropos of the current debate on Planet GNOME, sparked by Davyd, regarding the “dumbing down” of icons. Again, there are valid arguments for both sides, and again, you can’t please everyone.
More interesting (to me) on the planet were some sexy  mock-ups and works-in-progress on futuristic desktops. There’s Novell’s “December” GNOME mocks, Jon “desplesda” Manning’s Lazuli mocks (is Lazuli as in Lapis-Lazuli a play on Topaz?) and Symphony OS’s Grey Paper (PDF). I think that I’ve previously mentioned the Gentle GNOME mocks. Finally, last year I also made some mocks, which was discussed on desktop-devel-list.
Update (2006-02-06): tab icons (favicons) as the window icon is available as an Epiphany extension.