3 It's probably impractical to put your entire user folder in Dropbox, but you can put the most important folders there: The Documents folder is an obvious one. The Music and Photos folders might work if you have enough Dropbox space. (Remember, you can upgrade from the 2GB that Dropbox gives you for free to 50GB [$10 per month] or 100GB [$20 a month] paid accounts.) Create symbolic links to those folders from your various machines, and you'll have essentially the same Mac wherever you go.
4 If your hard drive is especially small, make room on it by moving some of your files to Dropbox.
5 Many of us store the files and folders for active projects on the desktop. Put them in Dropbox instead.
6 Scan important personal documents--your passport, driver's license, marriage certificate, and so on--and store the scans in Dropbox; that way, you can get to them anytime you need to provide a copy.
7 Archive the original installation files of your apps so that you can install (or reinstall) them as necessary on any of your Macs.
8 Download PDF copies of the user manuals for products you own--appliances and home-entertainment equipment especially--from the vendors' Websites, and then save them all to Dropbox.
9 As long as your music collection is small (or your Dropbox storage allotment sufficiently large), store your iTunes media in Dropbox: Create an iTunes Media folder in Dropbox and copy your media files to it. In iTunes, go to iTunes ▶ Preferences, select the Advanced tab, and select the Dropbox folder as the iTunes Media Folder Location. (You shouldn't sync the iTunes Music Library.xml file; doing so can reportedly make iTunes unstable.)
10 Synchronize Address Book contacts by moving the ~/Library/Application Support/Address Book folder to Dropbox and then creating a symbolic link from its old location to its new one.
11 If you use an inventory app such as Home Inventory or My Stuff to keep track of your belongings, save its data files in Dropbox. If the worst should come to pass, you'll have a full list of items to refer to for insurance purposes.
12 Several third-party utilities--notably 1Password and TextExpander--let you store their data files in Drop- box; you make the change in each program's preferences. Even if there isn't explicit Dropbox support, you can sometimes synchronize an app's data files by (a) finding out where those files are stored and then (b) using the symbolic link trick to move them to Dropbox.