According to some Italian software enthusiasts, it is possible to flash your G1 with their SuperHERO ROM, a port of the HTC Hero's firmware. Aside from the OS skin's beautiful graphics and animations, SuperHERO will activate G1 multitouch that allows you to zoom into webpages a la iPhone.
Of course, Bluetooth and Wi-Fi aren't all that functional with this firmware, and the OS can get a bit laggy and light on memory. So you'll need take the good with the bad should you decide to hack your G1. [HD Blog via androidguys]