I made this little AppleScript today which I’ve personally found to be very useful. On my Mac I have it so the script is activated by BetterTouchTool when I do a 5 finger tap. It will take a screenshot of a specific area, upload it to Dropbox, and copy a convenient bit.ly link to your clipboard. So here it is for your enjoyment:

    set filename to do shell script "date '+date-%Y-%m-%d-time-%H-%M-%S'"
    do shell script "screencapture -i ~/Dropbox/Public/Screenshots/" & filename & ".png"
    set dropboxurl to "http://dl.dropbox.com/u/[dropbox id]/Screenshots/" & filename & ".png"
    set tinyURL to (do shell script "curl --stderr /dev/null "http://bit.ly/api?url=" & dropboxurl & """)
    tell application "Finder" to set the clipboard to tinyURL

If you want to use this you have to replace [dropbox id] with your Dropbox ID number. You can usually get this from any link to a shared file, for example my ID of 3759922 can be found in the url https://dl.dropbox.com/u/3759922/Screenshots/date-2010-02-02-time-23-24-48.png

EDIT: @joshbetz came up with a better solution for this tutorial. Go check it out!