I used this method (Terminal) to set a selected folder on my Dropbox, so I have access to my screenshots both at work and at home.

BONUS: If you use Cloud app, you can set your screenshots to auto-upload and you get a link to it in your clipboard memory. Makes sharing very easy.

http://osxdaily.com/2011/01/26/change-the-screenshot-save-file-location-in-mac-os-x