I don't own one, but I've ridden them several times... My friend actually bought his girlfriend a 500 recently, and he just traded in his CBR for a Z1000. I tell you, I have that effect on people. I can be very convincing to come over to the Kawasaki side.
The 500 feels pretty torquey, and it's pretty upright compared to mine.. but I really like it. It's a lot like the 250, but a bit bigger and a bit faster. Fun!