You can use Dropbox and symbolic links. I have both of my macs syncing the Desktop, Documents, Pictures and Music folders setup like this. As stated, you will need enough room on your Dropbox account to allow that however, I purchased the 50GB and may even need to upgrade to 100GB at some stage.
It works quite well.. I create a new file on my desktop, and within seconds it is replicated on the other Mac. I delete it, and it dissappears just as quick.
In order to setup symlinks, you will need to do the following:
1) Pause dropbox syncing on both computers
2) Open terminal on both computers and configure the same symlinks
3) Un-pause dropbox syncing on both computers
Symlinks example (off the top of my head, you may need to research further):
ln -s /Users/Username/Folder /Users/Username/Dropbox/Folder
EG: ln -s /Users/eliehass/Desktop /Users/eliehass/Dropbox/Desktop
I would test it one folder at a time so that you know whats going on, start with your desktop for example (take a backup of it first in case). Also be aware of how long it will take to upload GBs of data to Dropbox.. mine took a few days to complete the first initial sync (uploading to Dropbox) - LANsync feature enables quick download speeds however to sync files locally (it will still goto the Dropbox cloud however).
Be ware though... If you enable this on your iTunes folder you can only have ONE copy of iTunes open at any time on your Macs.. the process would be to close iTunes, wait for Dropbox to sync the XML library files on both computers before opening iTunes on the other Mac. I also wouldn't be using this to sync Library or System folders.. I havn't tested that as I only use it for replication of personal data not system/application data, so I wouldn't know if that would work or not!