For months now I haven't been able to use Synergy between a Windows 7 machine and a Mac. The Windows machine would connect but no keystrokes would be sent from the Mac. The mouse, though, worked fine.
Apparently at some point I had unknowningly upgraded Synergy on the Mac (installed through homebrew) to 1.4.2. Today, per this thread, I downgraded to 1.3.6 and like magic, it all works again. That bug, sadly, has been open for two years. How can you promote software as "beta" and higher than the "stable" builds when a huge bug like that exists?