I just got my phone upgraded to the developer release of 3.0. It’s nice, I haven’t found it particularly slower than before, which I was worried about.
Tethering is awesome. The MMS and cut and paste has been implemented very well.
I haven’t encountered any major bugs yet either, although it seems other have. My biggest problem is that with Optus I cannot as yet mms and use the internet. I have to change the APN in the settings to the appropriate one for either task and then restart the iphone. So basically I don’t actually have mms working. But we are still a while from the the official launch and I am sure optus and apple can work it out by then.