My wife and I each have a 2006 'S' convertible as our daily drivers, and we've been very happy with them. 80k miles on mine, 60k miles on hers, and no out-of-warranty repairs on either car. We did have a few of the common problems (leaking thermostat housing, leaking engine mounts, etcetera, but that was all early in the warranty coverage.

I have a motorcycle and we have a 1983 Dodge Ram that gets used 2-3 times a year for "truck stuff" - i.e. hauling stuff to the landfill or picking up plywood from Home Depot, but we really haven't felt constrained at all using MINIs as our everyday cars.