GrabBox auto-saves your Mac screenshots to Dropbox
Think about that for a second: in one fell swoop, you've captured and uploaded a screenshot and grabbed the link for easy pasting. I thought no screenshot sharing app could be more efficient than my beloved Skitch, but GrabBox has proven me wrong. It should go without saying that a free Dropbox account is required to use GrabBox, but aside from that, the setup is a piece of cake.
Oh, and don't worry -- GrabBox lets you keep screenshots that you don't want to share from being uploaded, so you don't have to be paranoid that your secret robot shark blueprints might inadvertently become public.