With Syncplicity, at setup, you simply mark "My Documents" as a folder that Syncplicity syncs.

If he's interested in backup: Carbonite. $55, unlimited storage, and basically idiot proof. Use the code "100" to get 14 months for the first $55.

If he wants to keep his files in the cloud (access anywhere), with automagic sync, then Dropbox.

I use both.

I'm using http://www.crashplan.com/ for nightly backups. I have it set to back up arbitrary folders from three computers, including a 500GB iTunes library (it does differential backups, otherwise the nightly backup would take a month :) ).

It's not great for syncing, though. For that I use http://www.dropbox.com/. It's a bit of mental effort to remember to use ~/Dropbox for documents, but I manage.

I also use https://github.com/ for source code, but that's a very specialized tool and probably not what you want.

maybe this will help:
http://www.cultofmac.com/run-dead-ea...k-how-to/37898