i visited my brother last night and he threw on the xbox. it forced an update. then it downloaded almost a gig and threw an error. then it started again and installed and rebooted and installed.. about half an hour later we'd moved onto other things and never even played it. answered my question about whether or not i wanted one though! lol
PS4 updates are notably bad, since they do a full copy & write (vs write-in-place) on patches. It's good if there's an issue on updating, since you can delete the partially-updated copy and start over, but bad because it requires more than 2x the disk space for the patch.