I've been using Synergy for just over 3 months now and simply love it. I use to use a KVM but found the image quality to be really bad when using it.
For anyone whose been having the error'WARNING: failed to connect to server: Time Out'. Try changing the connect to name on the client machine to the IP of the server. For some reason my Windows PC name was not working but the IP connected instantly.
You may even want to manually set your IP to always be that number so it will never change when the DHTP tried to issue a new one.
Hope this helps some one else out there.
Update: If you're using a VPN and your connection to the server machine gets dropped, you must disconnect from the VPN in order to reconnect. This was causing some headackes for me a while back.
Also, if you're having trouble with Synergy capitalizing characters or holding down the Ctrl key, this post should help you out.