Aperture has
some of this ability built-in. If you make changes in one library, and attempt to import it to a second library, Aperture will just sync the changes. I'd encourage you to read up on the documentation on this area.
I have a little trepidation recommending it for a solution for everyday sync. But it's certainly something I encourage you to check out and investigate it, though if it were me I'd do initial experimentation on some trial libraries.
And I have
much trepidation about using something like ChronoSync to do this. They simply don't understand Aperture's library structure, and frankly I think the chances that you'll eventually corrupt the database (say if you forget to close Aperture on one machine and then sync) over time are very, very high.
