I had almost the exact same thing happen. The family workstation that the kids use for homework went 'T-U' via HD failure. Replaced HD and threw down 12.04. Just released it back to the kids with user accounts setup, everything brought up to date...that was it. They started using it (12, 9 and 9) and had ZERO problems with it. May as well have been using it for years. The only real comment was the lack of MS Orifice...err, Office.
So, they are all now running Thinkpads of their own, each with 12.04 loaded and have zero issues.
To each his or her own I guess.