iPhone 3GSes now ship with a chained-down boot ROM, intended to thwart jailbreakers at a fundamental level. It's already been cracked. But for what it's worth (seriously, what?), it has made life outside the App Store a little less convenient.
The Dev Team has struck again, negating the security work of the iPhone 3.1.2 update. Looks like it'll work even if you've never jailbroken your phone before (though soon-to-be-released hardware may not?). Pwnage can be attained here. [Thanks, SE!]