i own the g1 (rooted and customized to hell and back) and the mytouch 3g and honestly since popping my sim card into my mt3g, i havent looked back, i do miss the keyboard at times but i loaded the HTC IME onto it and its not bad, i also have 92 apps installed with 182mb of memory left, as well as hooked up PDANET app to my computer and mt3g for wired (sadly) tethering, this all being said, the biggest advantages of root access (at least IMO), space and tethering are solved...
Sadly i do miss all the system wide themes and some apps that only work for root, but i will say this, the mytouch 3g runs 2x faster than my g1 cyanogens latest build, the browser speed blows my mind on the mt3g ( i live in EDGE only for now, come on tmo get some 3g in cincy.
but for the average non tech geeky user like myself, the mytouch 3g is much more appealing than the g1.. for one it looks a ton better, i have the white and i think its one of the best looking phones on the market. For two it has lots more room for apps than the g1 and is more of a mass market design rather than the g1's geeky super functional but super fugly looks.
i bought the mytouch because i wanted to give it a true shot and maybe send it back if i didnt like it however, i love it and am gonna keep it, which doesnt mean i am getting rid of my g1. but what excites me most is this is androids first delve into possible mass market appeal, i mean with apps, the corp. email, the packaging, the marketing, the looks, and the accessories, the mt3g has positioned itself to become a pretty popular phone and what that means for us nerds, is more developers and better apps.