I've only had it for a week or so. Eventually I may find something wrong with it. But so far it seamlessly syncs computers, shares files between multiple users on different platforms, and other cool things. For instance, the way it instantly creates photo galleries. Add a photo, remove a photo? Instantly it updates your online gallery. You can even host an entire website (static html).

And it does all of this without behaving as an app. As an app it's pretty much invisible to you. You just think of it as a folder of your own files to manipulate within your finder.

It's easy on system resources, too.

Photo Gallery Index Trick
If you have multiple galleries (folders) inside your photos folder, each with it's own web address, you might try this:

1. Put all your picture folders inside another folder and call it 'gallery index' or something.
2. Now put 'gallery index' inside your Photos folder.

You now have a web page that displays an index of your galleries, each with its own thumbnail link. Sweet.

Lots of other Dropbox tricks & uses to be discovered I am sure.

The only caveat I have one week in is that Dropbox updates itself automatically as new versions are released. I don't believe that this is a preference that can be turned off. (Doesn't bother me, though.)