I think they're a good example of selective breeding, the things that characterise the breed (the head carriage, the long back, the "uphill" build) seem to have got more and more extreme. I don't like them if I'm honest, to look at I mean. I've met four or five and they were all lovely characters but of the three I rode I didn't find any of them very comfortable - especially in trot, it's SO bouncy it actually hurt my back.
There's a good history of the breed on here -
http://www.friesianhorsesociety.com/Friesian_history.html