For any file in your Dropbox folder, this workflow shows the dropbox short link URL (e.g. http://db.tt/1LkWGVJF) and copies the link to the clipboard (Cmd+Shift+D):
1. Select a file in Finder (must be a file within your Dropbox folder, e.g. ~/Dropbox/Photos/MyPhoto1.jpg)
2. Press Command+Shift+D
3. Authorize the workflow to use the Dropbox API (only if this is the first time)
4. The shortened link pops up and is copied to the clipboard.
It uses OAuth in the background to connect to Dropbox so you can authorize the Alfred 2 Workflow without storing passwords insecurely. For those who are interested, it starts a Ruby-based local web server using Sinatra which is then opened in the default browser. You can authorize the Dropbox app in your browser, and then the local server shuts itself down. Once authenticated, you don't need to do this step again.
Once connected via OAuth, this workflow has the potential to do a lot of things with Dropbox, but currently only queries the dropbox service for shortened URLs. This method (using OAuth/dropbox) has the advantage that any file in your Dropbox folder can be shared, not just those in the "public" directory (a deprecated method of accessing dropbox files).
The downloadable workflow itself is here (on dropbox, naturally):