See The DropBox Manual. It makes for interesting reading.
In some ways, I have always preferred what is described as "Microsoft’s sync solution." It "doesn’t rely on a central server but instead lets computers sync directly with each other." I recently updated to Live Mesh. The only problem, it does not work with mobile devices such as the iPod Touch or Android. In fact, it does not even work with Microsoft XP (as Live Sync did).
So, I use both DropBox and Live Mesh.