I've been, allow about 3 hours, there's plenty of amazing paintings there to see. Make sure that once you're done you walk up the road to the rijksmuseum - absolutely huge, amazing collection of art, one of the best museums I saw in Europe. Give yourself up to a day there. Don't forget to watch some diamond cutting at one of the many factories, visit the red light district at night (quite a sight), and travel on the trams. You can also visit Hooters (or a take off of) in the main street if that's your kind of thing. The Holland Casino in Amsterdam is worth a visit if you're in a gambling mood, reasonably friendly, and not too much heat. Table games better than slots here.