Among my hobbies is writing fiction. When I travel, I often tinker with drafts or make whole new stories. However, the notebook computer I use when I travel isn't the one I use when I'm at home (which has a larger screen, and as of this month also a second monitor). So as I move from the desk to the living room (where the notebook lives while I'm at home) I end up editing recent drafts on both machines, and losing track of which is more recent. That is, I edit both the A and the B version several times before realizing that each has SOME edits I want to keep, and neither can be thrown away, and I need to figure out how to reconcile multiple totally different solutions to various issues in troublesome scenes.
Then, when I'm on the road working, I might edit a file with billing information. And when I get back to my desk, I might go to work on another project and edit the same file on my desktop machine, changing a different client's sheet in the same file of billing records. And I have the same problem: inconsistent versions, neither of which I can just throw away, requiring hand synchronization. Oh, the humanity.
DropBox has a solution. DropBox is a remote-backup service that is so simple and so powerful you'll not believe the first two gigs (that's not MB, that's GB) are free. (Actually, there's an offer that gives you an extra 250MB with this link, and gives me some extra storage, too; so maybe it's 2.25GB free.) When you set up DropBox, you tell it where you want your synched folder to be located on your local drive. You need not place anything in subfolders that are accessible to the world, though if you have a brochure you want everyone to be able to download you can certainly make it publicly available (or your trip photos or the portfolio you'd like to show prospective clients). But let's but to the good part.
You save things on your local drive like normal. Things you save in the DropBox folder (or any subfolder) get synched to DropBox' cloud, where it offers remote backup for free for the first 2 (or 2.25) gigs. But you can set up your DropBox account on more than one computer. When you change, add, or delete a file on one of the computers, DropBox updates all your other computers using the same DropBox account. You get immediate synchronization over the web for the little parts of your files that are different. No more inconsistently-edited differing versions on all your machines, ever. And free backup to boot. Gigs of it.
Yes, 2GB won't help a professional photographer or an audiophile with losslessly recorded music -- but then, 2GB is just what's free. Try the service's 2GB-for-free deal (or 2.25, while it lasts), and learn why John Gruber thinks it's the best thing since floppy backup. With it, he approached a hardware failure without fear of losing ten days of work he did while on the road, because he had internet while he traveled and that meant he had DropBox protecting all his new work.
I've rearranged my folder for work so that my work in progress is all on DroBox so I have the current versions of active projects synching across all my computers, and I think that at free there's little reason not to try it out. In only a couple of weeks, I've already begun noticing the benefit of synch, and I look forward to enjoying the security of troublefree off-site incremental backup.
The remote backup isn't magical, so there's some lag on synch -- especially for big changes. However, DropBox uses custom icons that tell you whether each file has been synched since its last local change, so you never wonder whether you're fully backed up. And that's a nice feeling.
UPDATE: When synching across different computers, it's easy to (a) have the DropBox folder in different places on each machine because of the mood you were in when you installed DropBox on the different machines, (b) have file handles that are different under HFS+ on each file system on each computer so that an "alias" file will simply not work across machines, or (c) have a path that is different because the volumes on your different machines have different titles. John Gruber teaches us that there is an answer: use symlinks, not aliases, for things you want backed up that other programs expect not to find in the DropBox folder. The symlink will be right on each computer on which you make it, and DropBox will just take care of itself.