But only for stock SSDs apparently:

The new native TRIM support does appear to limited to stock Apple drives, as users who have installed third-party SSDs into their machines have reported that TRIM is not enabled by the update.

Moreover, the developer preview of Lion, which has always had TRIM support, does not support user-installed, 3rd-party SSDS either. Well, at least not on this machine.

10.6.8 Brings TRIM Support