I had the M500's on my last car (Mazda6 Wagon, size was 225/45/17 94W).
Overall I was very impressed with them. They are very sticky on both wet and dry. Other things that I recall are that the sidewalls are extremely stiff and they are also very heavy tires (much heavier than the stock Michelins on my 6).
Compared with other Ultra High Performance Summer tires, they would seem to offer excellent performance/$ (mine were $105/tire). When I eventually upgrade to 17's, these will be high on my list (I would keep the stock wheels and BFG Traction T/A's for winter).
Overall I rate the M500s as excellent in performance and top value. It is the best summer tire I've put on any car I've owned. The S02s would be second. Equivalent performance but twice the price. My previous favorite tire was the P7000s. They had excellent performance also (slightly less than the S02s) but were a bit more cost competititve.
The M500s are definitely a top performer. The sidewalls are stiff, but that is important to me. Overall grip is equal to my yoko a520s which were the stickiest tires I've used to date. I also agree with the wet weather performance comments above. Excellent.
Don't let the price scare you. These tires are seriouis contenders.
I used European Avons on my FXT last year, the ZV3 in 225/60/16. They were great, and I will probably mount another set this year. I drive very hard in mountainous and sometimes very rough conditions - and the set lasted nearly 50,000 kms!
They could handle my need for speed, and kept me quite safe even in the wet. I will look around for something better, naturally, but I doubt I find anything else.
By the way, my winter tyres are Blizzaks and I am also quite happy with them.