3.0 requires iTunes 8.2 (I had to upgrade). My phone was not previously jailbroken, I think I'll do that after the MMS update comes out. Ober, I would definitely hold off updating for you until the JB community has a chance to work out all the kinks, although I read one of the groups will have a jailbreak released Friday.
@Mike - The personal developer license is free (simply requires and Apple account) but you cannot apply or get your app in the app store. The limit might even be as low as 10 iPhones though. I'm guessing all of that is handled in the DRM (but you might be able to release the source and have others compile it for their own use). I'm still trying to figure out how to get my hands on a Mac to develop with. My first Hackintosh attempt got foiled by hardware issues (networking). Since it's a developer account, all you do (as I understand) is transfer the app to the phone from the SDK tools and run it. Change it to your hearts content and repeat the process. To 'distribute' it you just need to provide a link to it for others to install from.