I bet you thought the iPhone 2.0 firmware was all about whizbang new features, or the App Store. Well, it pretty much is, but it also includes some security updates. Apple has posted a KB article
that details all the security improvements that are baked into the 2.0 firmware. It is well worth a read if you're paranoid like me (most of the improvements deal with websites that are crafted to cause mischief on your iPhone).