I have a pretty average synergy setup. My main synergy server is on OSX (10.8) and my synergy client is on a linux box (Fedora 19). Any synergy user can understand how convenient it is to use: you start up the server and the client, and you can seamlessly move your mouse and keyboard between all of your screens.
When you first start it up, things work mostly great (there are some clipboard issues copying from server to client, but that is another issue). However, things can get a littley annoying once your displays have gone to sleep. After waking up from sleep, the synergy client will often have drastically altered mouse speeds. The mouse, at this point, will become too fast and sensitive to use practically. Unfortunately, this is a bug in the synergy software, and as of this writing is not yet fixed.
The most practical (yet unsatisfying) solution to this problem is to simply restart your synergy server. The client will automatically reconnect and your mouse response will be back to normal.
It's an ugly workaround, but until a proper fix can be implemented, it's the best option at hand.