Yeah, I did that with my G1. The main reason, though, was to help with speed through the memory and CPU usage optimization the Cyanogen MOD offered. The trade-off is that my phone started getting pretty flaky towards the end there, and I always suspected it might be due to the rooting I did on it.

I used the WiFi tether fairly often, which essentially turned my phone into a MiFi. The problem, though, is that I couldn't connect to it with my Zune HD, because the phone hardware/software is apparently only capable of doing ad-hoc wireless.

*edit*
One of the other nice parts about rooting the G1 was that I got many features of Android 2.0 that hadn't gotten to the official G1 phones yet. But now I have the Nexus One, which should be the first to receive any future updates, since it isn't held back by the carrier.