WMP has never visibly crashed, and there are no WMP related errors in the log(s).
The problem isn't just new files moved to the folder not showing up. Often files that have been deleted or moved out of a folder that's included in the library will continue to show up until deleted manually from the library, or WMP is opened and closed
several times, or I move files out of and back into the folder. In the worst cases the old files hang around undeletable and require rebuilding the library / deleting the wmdb files to clear.
Windows media library just seems to have a lot of problems keeping the 'library' in sync with folder contents. That said, I'll take WMP/Library any day over the nightmare that is iTunes...