I don't think I'd go with CM if I had a Nexus, since it's just pure Android. I was sick of Touchwiz, and finally went for CM10 the other day. What's cool is in addition to nightly builds, they have monthly builds, which are considerably more stable. I haven't had any issues, and really like it so far. There's also the fact that without CM, I'd still have ICS for quite some time. I liked ICS since I got it in April (thanks to a leak of the official ICS that gave it to me three months before AT&T pushed it out), but I wanted to try JB and this seemed the best way to do so.
Ultimately, though, what made me finally decide to take the plunge into CM? I can now go into the About Phone menu and upgrade from there. You don't have to flash the new build, it's as simple as official upgrades...well, I'd think. I never actually had an official upgrade.