I've just linked you to the high-level skinny, but there are a few really cool features worth highlighting, including Ruby on Rails support. From a pure tech perspective, DB2 9 greatly improves XML performance, and its new compression technology can help cut storage costs by up to 80% (Register for the Webcast to learn more about the potential storage savings.)
And just to prove there really are actual living, human beings who develop this stuff, and not a bunch of droids locked up in an underground bunker 1,000 feet below Armonk, we've agreed to bring some of them out into the fresh air to chat with the world. Be gentle...they frighten easiliy. And before you pummel them with questions, you might want to check out the DB2 9 demo.