I'm currently trying DisplayFusion out (trial) and I really like it. Have been using UltraMon for several years now but DF absolutely is rocks in comparison!

I do have one gripe though:
I usually work with multiple boxes (normally two PC's and one Mac) so I use ShareMouse (http://www.keyboard-and-mouse-sharing.com/) to avoid having to switch between multiple keyboards and mouses as I alternate between the different boxes. In that setting DisplayFusion acts up with the following two symptoms:

1. The DF multi monitor task bar flickers when I move the mouse cursor out to a different box.
2. Sometimes, after having switched to a different box and then re-enter the DF box, the Start button on the multi monitor task bar no longer works at all.

None of these issues will prevent me from replacing UltraMon with DisplayFusion but I just wanted to bring some attention to them.

Cheers