There is still the 'quicksynergy' package that depends on it. Has that maintainer been notified?

Replying to [comment:1 notting]:

There is still the 'quicksynergy' package that depends on it. Has that maintainer been notified?
He's most definitely aware of this, and since the synergy-plus packages will also provide "synergy = %{version}-%{release}" (the fork picked up the versioning where the original died off), everything should be transparent.

The relevant entry for quicksynergy : https://bugzilla.redhat.com/show_bug.cgi?id=524910

The one about synergy-plus : https://bugzilla.redhat.com/show_bug.cgi?id=538179

Also, am I correct to assume that for "current" branches (EPEL, F-10, F-11 and F-12) the right thing to do will be to introduce the obsoleting synergy-plus package as an update and nothing more?

OK then, blocked. Thanks for the info.

Yes, the simplest method for older branches is to just introduce an obsoleting package.