Nothing is ever 100% in the mixed up soup that is Windows, hardware, drivers, and applications.
So far no one has reported any problems. Rhino was obviously not developed on Win 8. That said, if we do find problems, we will dix them since that's the current version of Windows.
John Brock - Rhinoceros
I have this problem on win.8...my system is a - Asus K95VJ Laptop (Geforce GT635M, I7 3630QM, 12gb - ram,) ....after installing Rhino 5 (Evaluation) - right click does not rotate the view-port, actually I can't draw anything because the view-port are blocked or something like it - I can only access the menu and toolbars - or commands are working with a very big delay...