I don't mean to say that there's nothing to be happy about regarding the features of Cupcake. It's just that it's been hyped so hard for so long (I am not exempt) that I doubt the software can maintain the stir that has surrounded its release or live up to public expectation and justify everyone's anticipation. Don't expect it to make coffee and automatically shoot deadly lasers at insects. Those features are currently in beta.
Nevertheless, I am happy to state that T-Mobile has finally, truly, begun the official over-the-air updates. But for those who just don't want to wait another hour, it is now possible to update your G1 with the same US update that's being beamed out by T-Mo. The last manual update utilized the UK version of the software. So this might feel a bit less risky... and hacky, if you like.
There is still a chance you'll mess up your phone. So I'm not recommending this - just pointing you in the right direction. There is a step-by-step over at Android Rights. The file is provided by JF of xda-developers. Again - what you do with your phone is your responsibility.
Meanwhile, Haykuro - who ported the Sapphire (Magic) ROM for G1 owners just a few days ago - has already assisted in providing the world with the files needed to root the HTC Magic. That's for folks who already know what they're doing. Mmmmmkay? As for myself, I'm waiting on the Hero ROM.