I use a file synchronizer called "File Synchronizer" and it works quite well for what I do. There are numerous others available form the apple website under "System/Disk Utilities".
If you are comfortable on the command line, you can protect yourself from accidentally synchronizing the wrong way by doing the following on the "Master Library" that you want to copy over to the other machine;
1.) Open a Command Line Interface
2.) cd ./Pictures
3.) chmod -R u-w Aperture\ Library.aplibrary/ (Recursively remove write permission for the owner)
This will change the aperture directory and all it's contents to read only so it can't be accidentally changed. Then you perform your sync and change your directory back to it's original state with the following command;
4.) chmod -R u+w Aperture\ Library.aplibrary/ (Recursively add write permission for the owner)
You will have to do this on both the master and target directories as the file permissions will be copied over with the synchronization process.
Did I just brand myself as a geek?
Mike