Not sure how it is on Blur (I know it can be done).. but the steps on AOSP to include other groups:
Open contacts, Menu> Display options> (your google contacts email address)> Check the boxes of the contact groups you want to sync.
So.. Still zero need EVER to have BUA on the phone. Get rid of the dependency of another service syncing, and another complication...
Except I'm not talking about syncing to other phones - I sync to other devices in general - computers, Windows Mobile PDAs, etc. The sync solutions for all these unfortunately do not support Gmail labels (or do in a very limited fashion). I like the fact that my phone contacts are completely separate. If I decided to switch to a dumbphone again or some other non-droid device, I can happily resync my contacts at any time using BUA rather than messing around with other methods or relying on VZW to do it for me at the store. In any event it's personal preference. Some people find a use for it while others deem it completely useless.
Ideally, it should be a completely separate and all-inclusive apk that could be installed/uninstalled at will by the user, much like the facebook, twitter, and other apps available (not including blur or other vendor-forced garbage).