What helped you get quality feedback about your product?

I'm researching way's to get good (quality over quantity) feedback to validate our business proposition for experts and users over at www.thinkbase.com

What has worked well for your startup and why?

Our particular situation involves two types of users:

• Anyone with a problem
• Experts that have knowledge about that particular problem

But I guess getting good feedback is a challenge for any type of startup. Please share your best practices (or major fails!).

We'd be happy to learn and so may anyone else I suppose...