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.