I've been following Synergy for a while now, and find it to be an invaluable tool for my work environment. It allows me to move control between my OSX Lion, Windows 7 64-bit, and Gentoo KDE desktops seemlessly.
My only gripe comes when my Macbook Pro is situated left of my main Windows monitor, which is to the left of my main OSX screen.
MacBookPro LCD (OSX Secondary) --- HP LCD (Windows 7) --- Acer LCD (OSX Main)
Mouse movement can not handle this properly as it stands since OSX handles mouse movement between the two screens and currently doesn't consider there to be a 'gap' in between screens. As such, I have to deal with my laptop LCD assigned to the right of my main OSX screen, making it the right-most screen even though it is my left most screen (but least active). Otherwise mouse movement would go from far right, to far left, to middle as I move left. As it stands today, mouse movement goes far-right to middle when moving left, or far-right to far-left when moving right.
I read this slated to be addressed in version 2.0, and I can only assume it is by tricking OSX into thinking there is yet another screen in between my MBP LCD and the external LCD. We'll just have to wait to see...