I bought the pro 650's on recommendation from Head-fi.org a few years back.
I think they're great, like Bluesman69 says, very neutral, a little on the bass heavy side but comfortable to listen to for extended periods of time and detailed enough to mix, monitor, sound design, location record etc The isolation isn't too bad either and although they are still quite a big pair of cans, they don't make you look quite as dorky as a pair of Beyer DT's.
There's something to be said for the way the diaphragm is directed over your ears in these cans too, theres a plate over a large diahpragm thats projects the sound over your whole ear rather than soley down your ear canal. This makes them sound a bit more open with out being open backed, I personally like that.
They're made of plastic and rubber, but they have been everywhere with me for some time and stood up to a fair amount of abuse and they look like they would happily put up with alot more.
See if you can find someone or somewhere to have a listen to a pair, see if YOU like them :)