I've been working with Sharepoint on and off for the past few years and it's quite a love hate relationship. It's empowered me to do a lot of cool projects, but it's limitations and the way Microsoft has to come up with a special name for every feature drives me nuts. It's a good product that is a foundation for building other applications on and while the model is different than many other content management systems it's surprisingly flexible in most cases. There are some weird caveats to that - certain things that simply cannot be customized or simply cannot be configured in the way you would expect, but overall I think it's been a good platform for developing on.
What are your thoughts on Sharepoint? How have you used it to develop other applications or used it's built-in features?