There is a program called unison that is designed for sync'ng folders between multiple machines.
Rsync is only one way, but unison is more useful for desktop stuff. The one gotcha is that you have to careful that you only use one machine at a time and that you unify them before switching them. That is you use one machine you have to sync to the other before using it. Unison uses the same stuff as rsync, and is based on it, but it's more for keeping things in sync, were rsync is more for backups (but obviously it can be used also). There is a gui to unison and such.. for example if you use both systems before syncing them then certain files will be new, but different. Unison will call those to your attention and prompt you to choose what to do to fix the situation.
This is useful for machines that are not always connected. Like sync'ng a laptop and a desktop, which was what I used it for.
Something that is more useful, if you have multiple machines on the same network that are always connected to each other is that you can export the /home directory from one machine to the other using NFS. That way both will be using the same exact stuff and as long as you always remember to log out of one before logging into the other you shouldn't run into any problems.
This, in effect, is very similar to the roaming profiles feature in Windows networking, but a bit better. If you want to keep multiple copies of stuff, which is a good idea, then you can still use rsync to backup the /home directory from one machine to a backup directory on the other. In case the original system fails and becomes unavailable then you can just use a mount --bind or symbolic link or something like that make your backup directory the new /home directory on your remaining machine. This would get you the benefit of having multiple home directories, without the extra headache of worrying about synchronization issues. This of course depends on a constant network connection. So that you don't have to remember to sync stuff up you can use a cron job to automate the backups using rsync. That way you don't have to remember to do it.
If you want to get fancy you can also use rsync to do multiple copies or do incremental backups. For example if you do a full backup every month and a incremental backup every day, then that will automaticly give you multiple copies of any files or anything else your working on. This would give you some degree of undo or undelete. Something like that. It all depends on how much disk space you have, I suppose.
So there are a few approaches you can take.