The tires are the standard MINI Continental ContiTouring Contact all-season tires. They are non-runflat versions in the size 175/65-15.
It does appear to accelerate better. We can't tell any difference in handling in everyday situations. That would be different if we ran it on the track, but this is primarilly used a car for running around town and the roads are awful here in the area of San Antonio where we live. We'll probably replace them with a summer tire when they wear out. (May even do a little autocrossing to expedite the wear a bit!)
Where did I get them? I responded to a post to someone who was asking how much she should sell hers for. I'd been monitoring prices on eBay and told her what the recent sales prices were. Based on that post, someone e-mailed me and offered theirs. I didn't even have to pay for them until they arrived (his idea,not mine); it's nice to know people still trust each other these days!
I can't vouch for the weight savings being exact. Our bathroom scale isn't the greatest, but 52 lbs. is more than the equivalent of adding 3 horsepower (based on my calculations of about 15 lbs. per HP on the
MCS) and it does feel noticably sprightlier.