If you have an Apple Mobile Device (iPhone, iPad, or iPod touch) it's actually possible to sync it with multiple computers. You just have to understand the rules. Apple groups things into four categories:
Data – the data or info category consists primarily of things like your contacts, calendar, bookmarks, notes, email accounts, etc. This information can either be sync'd via iTunes or wirelessly via MobileMe or Microsoft Exchange (although Notes currently can only be sync'd via iTunes).
Media – the media category consists of your music, movies, music videos, TV shows, podcasts, audiobooks, ringtones, iTunesU and now iBooks. This content can either be sync'd or managed manually.
Photos – well this category is pretty self explanatory. It's your photo library and all of your photo albums. Your photos can either be in iPhoto or simply in a folders and subfolders.
Apps – last but certainly not least is your Apps that you've downloaded from the App Store.
Now that you know what the four categories are the content from these four categories can live on one, two, three or four different computers.
I have a mobile machine and having it run backups constantly annoyed me. I guess I'll switch over to something like SuperDuper or Backup.
Someone asked how to keep TimeMachine from running all the time. This happens when your backups are slow. So, in case it can help anyone else, here are a couple solutions:
You can edit the plist or grab TimeMachineEditor and drop the frequency down.
However, there's a better way. Make TimeMachine run fast.
Time Machine keeps one copy of every file it's ever seen, creates a new list of pointers to all those original files every time it makes a snapshot backup, and every time it runs, it compares your current computer's latest files against the previous list. Because of this, I've found the best way to keep hourly snapshots snappy is to:
1) In TimeMachine Options, exclude any constantly changing data that you don't really need a backup of. In my case, that's email. I use IMAP, mail is on the server, so I really don't need my local mail getting backed up every hour. This means exclude ~/Library/Mail. I also exclude ~/Downloads because presumably those files are available online, or if I want them, I've copied them somewhere else. Now I'm not wasting backups on .dmg files I'm going to install then delete. Some system files already aren't backed up, but even so I also exclude ~/Library/Caches, and definitely exclude ~/Library/Mirrors so I'm not backing up iDisk.
2) If you run any VMs, consider excluding their directories too, so you don't copy a 16GB VM image every time you change state in Windows. This saves an astonishing amount of backing up if you use Parallels or VMware regularly. Don't forget to back it up manually though.
3) If I make a major overhaul that drastically changes the content of my drive (for example, do something that adds then delete a large number of files), I usually consider wiping and recreating my Time Machine disk so Time Machine is not comparing a clean state against all those now missing changes. The backup checks through both current and past files, so if you deleted a ton of files and you don't need the backups you've made so far, go ahead and start your Time Machine backups over.
When I was backing up Mail and VM images, my backups took longer than an hour, and I hated it.
When I follow these suggestions, then the hourly TimeMachine run—even over the latency of WiFi to a TimeCapsule with its internal drive—is usually only a few seconds, and I don't even notice it.