Quoted from the Seaside mailing list...
After a beta phase of two months we release the final version of Seaside 2.8. Most bugs fixed during this period were either long standing (already in 2.7), minor or portability related, Together with the dozens of Seaside 2.8 applications already in production today this gives a pretty good feeling about this version. A special mention deserves Roger Whitney, thanks to him we went from 99 commented classes to 144.
We have a list of new features  and a migration guide  on our homepage.
Squeak users can get it either from SqueakMap, Universes or directly via Monticello (Seaside2.8a1-lr.518). A special note for Squeak users, do not load Seaside 2.8 into an image that has already Seaside 2.7 in it. If you use Squeak 3.7 you will have to load SeasideSqueak37 as well.
VisualWorks users can get it form Store (2.8a1-lr.518,tkogan).
GemStone/S users can load Seaside2.8g1-dkh.522.
Cheers The Seaside Team
I've been using 2.8 for a while now in development and for several weeks in production, it's solid and very easy to port to for 2.7 users. Upgrade as soon as you can, it's quite a bit snappier and uses much less memory.