There is a pair of Studio 150's on ebay now, in an auction that ends May 15:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1351071948
I have a pair of the 150's, myself, and agree with the posts above about them, they're absolutely beautiful and the sound is wonderful. They don't have as much bass extension as many other speakers in the price range but, for my taste, more than make up for it in musicality.
I recently spent a very long day auditioning speakers in the $3,000/pair price range, trying to help guide a close friend to a purchase. We heard several nice speakers from Sonus Faber, Linn, Vienna Acoustics and others but when we got back to my house I still liked my Proacs, by a good margin. I paid $1,300 used for a mint pair about a year and a half ago.
When I can afford something in the Response series I'll move up but the Studio 150's still surprise me every time I listen.