I like SVN. If you are familiar with source control software you can have it up and running in about 10min. I use it mainly because my buddy is a total computer newb (to the point where downloading and installing an addon for wow requires 30min over the phone.... EACH time). With svn I can modify/update the repository and he can make his addons directory match what I designate it to be.

However, I also use it myself. I play on my main box, then sometimes on my laptop. Occasionally I'll make a change (to addons, macros or whatever) on one of them, and need the change on the other. So I just commit to the repository when I shut the game down (which is when the changes save to your HD), and then update before I start playing on the other device. Also, when I make macros for my 5box. I write them on one box, commit, then update from the others. For me it is simply to do and use, for others it might not be.

I would also maybe check out the lazyboxer util posted here. Or maybe look into robocopy.

-S