btw, you can always do keyword research and check the searches at
www.overture.com and the results at google.
when you get the RS ratio (ie. results divded by searches), anything close to a one is good. (high demand (by searches) compared to low supply (by results)).
i've attempted to add more qualitative dimensions to the equation though and put some pointers in my blog post "
Internet Marketing Trendspotting: A Quick Guide to making a killing on Niches"