MVP works great with multiple UI. I do have some experience earlier on having an application both working on Windows and ASP.NET webforms and MVP was very handy to make this port without much pain. Though we had to put in lot of abstractions, but the end result was very satisfying.
Its another story that we are rebuilding the app on ASP.NET MVC (not due to any constraints with MVP) but due to the fact that we are moving towards one UI technology across all our apps.
But MVP did definitely helped us and also we did have some unit test which made the transition much smoother. Overall, you wont' regret having this pattern in place.
So, in a nutshell, if you are planning multiple UI, then its better to stick with MVP and you can easily scale to other UI like mobile, tablet etc.. without much work (if need be).
For the authentication we specifically created custom principal object which is used by both web and windows app. Yes we didn't use membership provider because we already had our own custom authentication system in place which played nicely with both technology.
You can provide a common abstraction for security over membership provider and use it in multiple place..
All the very best with your endeavor..
Rajesh Pillai, Mar 30, 2012