My experience with developing for Sharepoint was very painful. The jist of it was, unless you are truly going to hook into a lot of the core functionality of sharepoint (document collaboration and workflow) it will be MUCH harder to build an app to run in sharepoint than it would be to build a standalone application.
But MS has released some new extensions that will hopefully ease the pain a little bit:
Announcing: Visual Studio extensions for SharePoint – Developer User Guide
I don’t know if I will ever have enough time to implement anything in sharepoint, but these will be nice to have.