>This sounds pretty crazy, as a WinForm that is utilizing a Web Service might need to write data locallly (like store user selections, user preferences, etc.)
>
>Can anyone shed any light on this?
>

Sounds like a perfect scenario for Isolated Storage:

"Isolated storage is useful in many situations.
Downloaded controls. Managed code controls downloaded from the Internet are not allowed to write to the hard drive through normal I/O classes, but they can use isolated storage to persist users' settings and application states."

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpconscenariosforisolatedstorage.asp