I thought I had read IGN.com saying something about having few issues, but I can't find the article, so I may be wrong about that. In retrospect, it may have been an article about how well the initial release games work with 1080p. Anyway, Sony also has a site regarding bw compatibility here:
http://www.us.playstation.com/Support/CompatibleStatus
http://www.us.playstation.com/Support/CompatibleStatus