On a single-user machine, screwing up as root and screwing up in your unprivileged account is pretty much the same, since the most valuable you're going to loose isn't that 20 minute Ubuntu install, but your files. And the user you use, privileged or not, will have the power to wipe your files out.
Only other benefit (apart from all those programs that will complain or actually refuse to run as root) is if you run something questionable, it won't be able to install a root-kit, open a backdoor and hide the process.
This isn't exactly true. A vigilant user will run normal backups, and those backups will not be in a location that is writeable by the unprivileged user. In this way, it will not be possible for you (or an attacker) to completely wipe out your important files, only those changes from the last hour or so.
Based on an rsync-backup article that I bookmarked a long time ago (http://www.mikerubel.org/computers/rsync_snapshots/), I run backups of my important files (/home/, /etc/, /usr/local/, some directories in /var/, and so on) every hour to a /backups/ directory that is only writeable by root. Every day, I copy a backup over to another machine using the same rsync process.
Only other benefit (apart from all those programs that will complain or actually refuse to run as root) is if you run something questionable, it won't be able to install a root-kit, open a backdoor and hide the process.