Now since most know that Ubuntu 11.10 is certainly faster than all of its predecessors (and other GNU/Linux distributions in general, as far as I know) because it has an impressive 12 seconds of boot time!, but there are a lot to improve (especially the new and faster + a bit buggy USC, etc), so the upcoming Alpha 3 should be something "interesting".
Anyhow to brief you about what's new and other whatnots ...
*. It seems that Gnome 3.1 x pre-builds are already (some of 'em) available for Oneiric Ocelot + the Gnome team do have few major improvements of their own for the upcoming, 3.2 major release as well.
*. Compiz is updated to 0.9.5.
Although the actual or the original Compiz version is 0.8.6 (which many other distributions prefer) but this version "change" occurred because the Ubuntu developers decided to do their own improvements since Unity 3D depends on it so having a "Unity optimized" Compiz compositing manager makes sense.
But as many have claimed, it's a bit buggy at the moment (in 11.04 I mean). So hopefully this may have fixed few bugs and performance improvements :).
*. Firefox 6.0 beta (6.0.b3 build 2 to be precise).
*. Unity desktop module updated to 4.4 (current version in 11.04 Natty is 3.8) which include few of its own bug fixes such as - Metacity related fixes, drag-n-drop related bug fixes, Compiz related crash fixes, etc.
*. Switching from Gtk2 -> Gtk 3 which is happening slowly at the moment (understandable).
And many other Gnome 3.1x related application builds for the 11.10 Oneiric Ocelot updates are just a few to mention.
Anyhow, if Canonical can make Compiz a bit stable and fix performance issues with the Ubuntu Software Center (which is looking good in the 11.10 alpha version as said before), etc ...
... then I think the upcoming 11.10 might be one of the robust and fastest (at least concerning boot-time, which seems to be the "only thing that matters" in the current trend) operating systems that can stand up against the Google Chrome OS "being the fastest" challenge :). We'll see.