I'll briefly weigh-in:
I have taken my M3 tracking once. This is what I learned / gathered:
: it's true what they say - you won't appreciate the machine you're driving until you bring it rocking down a straightaway at 135mph and 8400 rpm only to drop anchor 300 yards out and coax it through a gut-turning, g-force causing hairpin at 75-85 mph. For what has a times been labeled both a "sedan" and a "cruiser," it's a hell of a car and you won't fully appreciate what you're driving until you take it to the track. Given the premium we paid for the M vs. a standard 3, it's my opinion that every M driver should take their car to a track event at least once. In some ways, it legitimizes the extra cost we plonked down the day we picked up the keys.
Beyond the experience itself - which I'd characterize as an amazingly fun (and terrifying) self-directed roller coaster - you learn quite a bit as well. I was fortunate enough to be paired up with an instuctor with over 20 years of racing experience. He was shouting at me the entire time while simultaneously encouraging me to go faster. Through 1 full day and 4 sessions, I learned quite a bit from him. I feel that I have implemented a lot of what he taught me into my daily driving routine, and to this end, the experience was additionally worthwhile.
In this video, you can sort of hear his muffled commands as I went around Lime Rock Park. He was on top of me the entire time.
Further to the above point, I think that it's imperative that any first-timers go to an event that provides instructors. It's my feeling that taking on day numero uno sans instructor would be tantamount to suicide. It's not so much about skill per se rather it's an issue of technique. The technique comes with instruction, and you don't learn it from playing Need for Speed
It's dangerous. My instructor was the first to tell me that you can do everything right, play by the rules, keep the speed in check, and still very easily end up in the wall. There are so many variables that are out of your control - for example, it is not uncommon for cars to dump some oil on the track. The oil is incredibly hard to see, and if you hit it, well, that's all she wrote. Additionally, and maybe stating the obvious here, but you are not the only driver out there ...
Through the 1 day and 4 sessions, one car did go into the wall. The guy didn't have track day insurance, and the car was totaled. Expensive day for your prototypcal weekend warrior type. His mistake? 2 wheels on the track, 2 wheels in the grass - he didn't realize it, hit the brakes - the difference in grip threw him into a spin that carried his car nose-first into the wall. Fortunately, he wasn't hurt, but his new car looked like an accordion on the back of the flat-bed truck. Apparently this guy was a very experienced driver - shit happens, however.
Before you go, you will most likely need to get fresh brake fluid and, if necessary, new pads. Additionally, you will have to find an event that provides instructors for newbs (like me). Lastly, and though I didn't do it myself the first time out, you really, really should think about getting track day insurance. With the insurance, you're looking at an expensive day. For example, the track day that I attended was $350 through BMWCCA. Add the cost of insurance, ~$400, plus cost of gas getting there + expended racing, factor in wear and tear on at least the tires, and you're realistically looking at $1000
to spend a Saturday driving like a loon. Unless you're filthy rich - and I get that some of you are - it's hard to legitmize this level of expense on, e.g., a monthly habit as unproductive as this one (haha). I guess that some of these expenses (i.e. the need for an instructor) would come down with experience; still, I can't envision attending a track event without insurance, experienced driver or otherwise. Seems like a monumental risk.
On the flipside, you dished the extra $ for the M, so why not enjoy it. Get the money together, find a good track with reputable instructors, and make sure you have your insurance for the day. Do it at least once - the experience will be exhilirating, terrifying, and educational all at the same time. Furthermore, you'll never look at your car the same way after - I know that I certainly don't.