We don't know exactly what's new yet, but Palm's released firmware version 1.0.4 for Pres on Sprint (not to say there are any other Pres out there at the moment, anyhow). Stay tuned for details.
Update: Looks like the only changes here address security vulnerabilities -- and interestingly, Palm gives a shout-out to Townsend Ladd Harris (a Pre homebrewer no less) who helped find them. Cheers to that.
Update 2: Sadly, Palm's plugged the hole that allowed homebrew apps on the phone without a jailbreak, though software you've already installed on the phone will continue to work. The hole that's been plugged was admittedly dangerous to leave open (installing apps via a link in email), though rooting and installing otherwise remain unchanged as far as we know.