First, I don't like OEM "skins." I started with bare Android on the OG DROID and have since had both Blur and Sense. Both got in the way and Sense felt heavy. Perhaps if I had started out with one of them, I wouldn't have felt that way about skins, but I do.
Second, I like the idea of Google managed updates. Even with the DROID, Motorola and VZW messed up the release process. Yes, I rooted and ROMed, but I shouldn't have had to to get updates on an unskinned device. VZW may still get in the way of the Nexus due to the whole CDMA kerfuffle, but it at least gets Moto out of the process.
I have unlocked and rooted my Nexus, but so far the only thing I've done that required root was to use Titanium Backup to restore some of my apps and their data (and continue backing up apps). I probably will ROM at some point, but it's less needed with ICS and no need to get rid of the OEM customizations.
well I guess I'll be the vain one here and say the real reason I got the gnex was the damn sexy screen and wanting to check out ICS, since I was coming from iOS I knew nothing other than the phone looked awesome.