I had an '02
MCS with 36,700 smiles on it when I traded it in on a new '06
MCS. My reason for trading up was only to get the newly offered LSD.
It was 100% mechanically reliable. It had a few squeaks and rattles that the dealer repaired under warranty.
Until the factroy mandated an upgrade to the ECU I had no problems with the dreaded yo-yo, stumble, or hesitation. After that the factroy never solved any of the problems in their subsequent software upgrades. I installed the VGS (vaccum gain system, you can find out more about it by searching on this site) and that basically eliminated the issues.
So far my '06 has not displayed any of the problems. Touch wood!
If you are used to driving an MG Midget you will be blown away by the MINI.