They look great for the money, but there were a few things that held me back from picking one up and going with the 5D3 instead. First, I don't want essentially the same AF as my 5D2. The center in the 6D is supposed to be great, but the outer points are supposed to be equal to the 5D2 (so not very good). Also, I use the joystick all the time, and I really don't want a camera without it. I also have really large hands, and I wanted the larger form of the 5D3. Finally, I wanted something with dual card slots. Looking forward to being able to shoot on SD and have everything backed up on a CF card.
So, I think it comes down to what you're going to use it for. I found the AF on the 5Dii alight, but I did get OOF shots often using outer points. I got tired of that and am looking forward to having an awesome AF system. That's worth the extra money to me, but it might no be to you.
Also, you'd be better off just getting a 5D2. You can find mint ones for $1100. If you don't need the high-iso performance, then it would probably be just as good as the 6D.