If you have a private "beta" group, you might also consider getting feedback via mockups. The benefit of mockups is that they are very early in the cycle (and thus still easy to change). I'll bounce screenshots of ideas on how I want something to look visually with maybe an explanation of how it conceptually will work.
A green light doesn't mean it is the right solution, just that it is worth taking to the next level. You may still find that once users can actually use it, the feedback changes significantly. That said, I find it's a great tool to validate that I'm moving in the right direction. -- Mark Munz unmarked software http://www.unmarked.com/
