One unfortunate complication with this is that using the phone without a Google account means one will likely miss out on security updates. As Google fights android fragementation by moving more functionality into user-upgradeable apps, not having a Google account means one cannot update things like Google Play Services. I imagine there are security fixes which go into those updates.
Of course, one could disable those specific apps. However, in the example I used—Play Services—disabling (or having an old version of) it means TextSecure's push messaging does not work, for example. Going off on a bit of a tangent, I would be interested to see a discussion between Moxie and Jacob about this aspect of things. Is it worth having a Google account if it means you have encrypted push messaging? Is is worth not having a Google account if it means you cannot have encrypted push messaging? (Yes, encrypted sms would still work without the Google account).
In the event someone points out the TextSecure APK is only distributed within Google Play, it is relatively straightforward to build TextSecure from source. So, not having a Google account does not preclude one from using TextSecure. And one can use the push messaging via Play Services without a Google account, provided a compatible version of Play Services is on the phone.