Third-party service that syncs preferences? Like MobileMe
I've got a system set up with Dropbox to do something like this.  I have several settings files (.profile, .gitconfig, ~/Applications, etc) living in my Dropbox, and then I run a script to iterate through them and set up symlinks to their appropriate location.

You could probably do something similar, perhaps even by symlinking your entire ~/Library/Application Support folder.