M cars are the ultimate BMWs. They are BMW's without compromise in terms of performance for the package they're wrapped in(excluding the new SUV-based M vehicles). But with the M3, M5 and M6, you're getting well thought-out platforms with race engineering dumped in for good and high-revving, naturally aspirated engines with big, fat tires to keep grip.
My Uncle attended M School a few years ago after picking up his E39 M5 and after hearing about it second-hand, I was sold within maybe 30 seconds. My buddy Horatiu, owner and managing editor of BMW Blog, probably the largest BMW-dedicated news site on the internet, hooked us up for a free trip to the one day M School.
We spent the morning in the classroom learning how to correctly balance a car for braking into a turn and how best to get a car back under control during understeer and the even more unfriendly oversteer. After that, we broke into teams and hit the track, my team in the M3 sedans first with the DCT (double-clutch transmission) to do some closed course track work and get familiar with the M3's handling before we jumped into M5's and the M6's to practice car control skills in the wet, learning what a 3,800 lbs, 500HP M6 will do with no stability control on and a generous right foot.
By the end of the day, I'd gotten the M3 well sorted out and logged a 23.38 second run on the closed M3 circuit after starting the session with a 28+ second run, so I shaved 5 or so seconds off of my lap times. Not bad! You can check out the article here on BMW Blog and I've yet to figure out how I can post a large gallery here so I'm working to post more pictures. Here's a quick tease with some low quality pics for now from Facebook here for Day 1 and here for Day 2.