Hi Greg,
The best solution for you would be using built in asp.net role management for your web application,depends on your applications complexity that how much can inbuilt role management handle for you.
Please check these links
http://msdn.microsoft.com/en-us/library/t32yf0a9.aspx
http://aspnet.4guysfromrolla.com/articles/120705-1.aspx
About Geneva, its a claims based access model which is being proposition from MS from long and finally we are seeing them. I have evaluated the Beta and seems to work fine , but dont know how well it can be used for production level code.
If you are looking for multiplatform federated applications , you can go with geneva or else the asp.net role management should be enough.
Again, it entirely depends on the complexity of application you are developing.Geneva can handle complex federated applications very well without writing much code.