I also had the coolant issue, I think around 65K miles. I saw the needle starting to creep and had already owned a BMW, so I parked at a Chilis and had it towed immediately; needless to say, the coolant reservoir and something else was cracked. I have had two BMWs prior, and you HAVE to watch that coolant needle in them, or you will be out a fortune (as someone else said, like $5,000 or more). The plastic radiator necks crack, or other coolant components, and you will blow the engine. If that coolant needle starts moving in ANY BMW, pull over and get it towed. They are calibrated to sit in the middle even if they are running slightly hot or slightly cold, so if it is actually moving, you're in triage mode and need to pull over.
For aspiring BMW owners, get the cars fixed at the dealer and buy dealer maintained cars. The newer cars are not designed to be worked on by non-dealers. Indie BMW shops don't have the tools or training, and they will try to learn on your car, and likely break something.
I bought a 03 Z4 3.0 in 04 with 7,000 miles. I love it for a summer car in Chicago.
Only problem I had was with the roof pump, which I read about and did myself. Be careful and do it correct the first time. Other than that, it's been great.
Replaced the tires with top of the line Michelin tires for a much smoother ride.
I bought an '03 ZR 2.5i 7 years ago and love my car.
I have had no problems, little maintenance and found a BMW shop that is honest and reputable. I love them! If I have a problem, they will get me in same day and fix it while I am sitting there (I had the coolant issue about 4 months ago and am at 77K - I paid 1,200, not 5K). I have to wait, but saves on tow charges!
If you are in Arizona, he has 2 shops. One in Tempe and Mesa. Babbitt Motorworks.