One of the frequent criticisms of Dropbox is that it requires you to store your synced data in a particular location--the Dropbox folder. You can place that folder anywhere you like, but anything you want Dropbox to sync must be placed inside that folder. Compare this with SugarSync, which lets you choose particular folders to sync, no matter where those folders are located. (The downside is that, whereas Dropbox integrates directly with the Finder and just works, with little to no setup, SugarSync's folder-picking feature requires you to use a not-so-simple screen in a separate utility to configure those folders.)