Check out the GNOME 2.26 Release Notes for all the new goodness that's been revealed in the latest release. Short summary is better disk burning with Brasero integrated, better file sharing with the integration of webdav and bluetooth, Evolution mail client upgrades, more PulseAudio integration, easier multi-monitor configuration, better IM (including video), lots of other minor tweaks.
Again it is (IMHO) an evolutionary upgrade, with not a lot of really new stuff or quite frankly, exciting stuff. It is good to see the improvements, improved developer APIs, internationalization, etc, but there's no huge jumps that I've seen, or really compelling reasons to upgrade. Of course I will, as I'm a sucker for pretty much any upgrades :) In fact, I'm looking for the Ubuntu packages now :)
Congrats to the GNOME developers and contributors on another great release!