not much. What kind of app are you wanting to distribute?
Normally, if you created your .net app without any specially licensed
components, you already have the licenses that you need. If the user needs
to have SQL Server installed, then they should purchase that seperately, or
you can provide MSDE with your app.
If you used components from a third-party company to make your user
interface more rich, or to use internet protocols more effectively, for
example, you may need to have a license to distribute these components.
Check with the vendor directly.
-- Nick