TIV  You might try Barquee (also on MU). It displays the information in the menubar... but it doesn't have all the options of Synergy.  
(Version 2.9)

TIV  Wow, quick response on that one. 2.1 fixes the problem I noted below. Thanks for the delay option, too!  
(Version 2.1)

TIV  I've used this for a while now and have been happy with it, but with this update, I've started having trouble in Safari. I like having it go to 40% when the window's in the background, but now it goes to 40% as soon as it launches and switching to another application and back is the only way to get it to 100%. Somehow it's taking the background setting and using it for the new window that pops up on launch, I guess. (I suppose it could be having this problem with other apps, too, but Safari is all I've noticed so far. Mail, at least, seems fine.)

If this is dealt with, it'll be a great extension again. Thanks.  
(Version 2.0)