I use it often via gflags to start on process startup, because WinDbg startup is a lot faster than letting the process crash, windows showing the error dialog, and then clicking in the visual studio version selector to select Visual Studio.
A few friends of mine that do memory forensics made extensive use of WinDBG to debug memory translation code. In the memory forensics developer community (yeah, very specific) WinDBG is one of the most reliable tools to use.