I just switched from an iPhone to the Nexus One, and I must say I like the Nexus One a lot. I do miss iPhone's intuitive and highly uniform user interface. However, the N1 offers several advantages that really appealed to me:
1. Excellent system wide implementation of voice activation AND input by dictation.
2. Google Navigation: it's basically 95% as good as a Garmin Nuvi system (no lane assist etc), with the addition of full internet
3. Excellent Google apps integration: Gmail, Calendar and even Google Voice all work seamlessly with the Nexus One.
4. Nexus One is fully unlocked: this feature is very important to me as I travel abroad and swap my SIM cards frequently.
5. Of course, the data tethering on Froyo is just too useful to leave the N1.