We are trying everything we can to make it less painful for the developers. Most of the time, the hard question is whether or not the P/Invoke signature is accurate. Now that we have a sample that shows P/Invoke signature for methods declared in Windows.h, it's just a start.
You can also find a list of resources that provides assistance to developers encountering problems P/Invoke functionality at http://www.gotdotnet.com/team/clr/bcl/TechArticles/TechArticles/PInvokeHelp/FAQ.aspx. Please let us know your feedback.