I can second this post 100%.
Synergy, InputDirector, etc. all have actual hotkey support - what Multiplicity has is frankly next to nothing.
I've found the multiplicity seamless KM to be quite good, it resolves some issues i've had with Synergy particularly on the M side and seems to have better performance than InputDirector, or other freeware but I actually still run Synergy in parallel with my client boxes arrayed without screen connection to the server just for the hotkey support Multiplicity is missing.
This isn't to say that Synergy has great hotkey support either, I have a 15yr old programmable keyboard with better hotkey support than Synergy - but it at least lets me bind a hotkey on the server box to send an input (or different inputs) to one or more client boxes. Even this very basic key-binding functionality would be a huge improvement and get on par with some of the competitors (cheaper / free competitors that is).
example - I press hotkey A on the server A, it sends X to client B, X to client C, Y to client D, Y to client E, Z to client F, Z to client G.
A more feature rich system that would be a market differentiator would be like what programable keyboard/mouses have but coupled to the input network multiplicity provides - where you can basically record input macros that can have multiple keys, time delays, logic, repeat toggle on/of, etc. bound to the server hokey that can activate a mini input program to client boxes.