The Dev-Team has finally released the Pwanage Tool for OS 3.0 (and meanwhile even a second tool called redsn0w) to jailbreak updated devices. First I had some problems with error 1600 and 1604, but after some search I have finally solved them and everything is fine! An iPhone without Winterboard just sucks.
One thing I really hate about the new update is that the "old" iPhone (2G or Classic) does not provide all the new cool features that were announced for this release. No MMS, no Stereo Bluetooth profile, no tethering, and so forth. In the end you will get a voice recording tool and copy & paste. Wow! Thanks Apple!