There've been a couple of times where I've responded to a wtb post before posting my stuff for sale, but on both occasions the buyer offered way under the price I eventually sold my stuff at. So basically, I stopped because I wasn't interested in negotiating more than a little bit below my target price.
I have listed wtb's before and have a price in mind...I think most people do. So it's just connecting with the right seller/buyer combo. If you want to buy something definitely check daily on the FS section.