I agree with the majority - a camera is totally unnecessary and as a nano-watch user, it would serve me absolutely no purpose. If it was on the front, then maybe, but it would be very awkward and possibly tiring attempting to FaceTime on it. It certainly seems futuristic in a sense, but I don't think it's a good idea.
I personally would like to see:
- bluetooth (for bluetooth stereo headphones)
- a thinner and maybe slightly concave design (again, I wear it as a watch)
- Wi-Fi/3G (I'm a heavy Pandora user)
- and a longer battery to boot.
- Maybe some way to interface with an iPhone or iPad would be cool too... notifications right on your wrist.
- Maybe use the nano as a remote shutter release for an iPhone (like if you were taking a group picture and wanted to be in it or something)
Certainly a design challenge to include all the aforementioned (probably impossible with current technology), but it would be insanely awesome.