I think there's been some good improvement on there over the last couple of years, and, as you have may read, Stanley Gibbons just bought it from the guy who developed it (and still runs it).
Some people have difficulty searching on there, but it's mostly because the search is so powerful, rather than so lame. If you have any questions, feel free to ask them on their discussion boards, or here, and someone will try to answer them. (Oftentimes, especially with search, the developer answers them.)
Full disclosure: I have a small store on there, but have been rooting for them a long time, because there needs to be a stamp-oriented site that's a viable alternative to
ebay.
Also, I just remembered, if you're a member of the APS, their stamp store is also a good source.
http://stamps.org/StampStore-- Dave