First, I know some turbos are quite rugged, as I had a 1982 Datson 280z turbo for 120k miles, from new. I drove it hard and fast, never a warm-up or spin-down.
Actually, it had a problem, where the oil seal would give out about 70k. They found out about it and extended the factory warantee. I had to replace mine at 80k. But it drove fine till I sold it.
Next, you should look around the forums using the key words Waste-Gate rattle and Turbo Lag. There were many threads for a while about how some turbo waste gate pivot points were failing, and how BMW reprogrammed the car to open the gates later. Which stopped the rattle but introduced the dread TurboLag. (Keywords progman 29.2). See
http://www.e90post.com/forums/showthread.php?t=186936
But this was a problem with the wastegate, not the turbo itself.