Good points, Cory...
...I've seen some of the same myself.
Add to that:
-Inadequate project sponsorhip. Projects that either consume people's time or will change the way people work need strong support from the top. Otherwise, people critical to its success will either ignore it, not contribute enough, or sabotage.
-"Big bang approach". If you try to build a mansion all at once, instead of small rooms at a time, that people can use and appreciate, several things will likely happen. One is that interest, cooperation and support will fade when people don't see something tangible soone enough. Another is that the people bulding the system won't share a portion of the solution with the client, have them use it and give their feedback for enhancements. This is necessary, because, as you mentioned, most users don't know what they want until they see it.
