You know that they suck, so I won’t elaborate on that point, but what about the memory leaks in .net framework?
We had an issue at work with our IISs going crazy and shutting down after a few days of operation. The sysadmin investigated and attributed it to excessive memory usage, having w3wp.exe reaching memory consumption numbers close to the theoretical maximum of a 32-bit process. This problem was postponed for a future investigation since there was no time to resolve it.