I drove an hour or so to pick mine up yesterday. Apparently in the US only the markets with active 3G got G1's. Luckily the store I went to yesterday was the only one to get any in my area. It was as easy as walking waiting three seconds and buying the phone outright. MY plan increased $10 with insurance and I've been messing with the phone for the last day or so.
Initial impressions:
UI is faster then most WM phones I've owned, but still not as responsive as the Iphone UI. Hoever I have not taken off the screen protector, I'm waiting for one from here ->
https://www.zagg.com/ Hopefully the screen will become more responsive.
there is a slight learning curve. If you're like me and adept at figuring things out without a manual it shouldn't take more then ten minutes to figure things out. You just need to mess with it.
I still feel like it's not as "open" as the WM platform, mainly due to being such a new OS I don't have access to things like File explorer and the like.
The build quality was better on my JAM and TYTN II. My screen creaks when I press in the bottom right hand corner and the screen is much like the Diamond but I'm still a fan of the Iphone screen.
Otherwise this phone is much better then my TYTN II.

For phones: T-Mobile G1, HTC TYTN II, T-mobile Dash, I-Mate Jam, Mitac Mio 8390, Motorola A630, Nokia N-gage, Nokia N-gage QD, Motorola C331g.
For the car: Air suspension, ICE, I/H/E setup, more to come later. . .
For guns: ICS M4 CQB Pistol, KJW Sig Sauer P226, maybe a M14 EBR or G36K later. . .
Now only if I could afford modifying my car and my mobile phone addiction. . .ha ha ha. . . uh oh add airsoft to it too. lol