Just as with image editing, the export architecture in Aperture supports a robust plugin ecosystem. There are lots of plugins available that allow you to send your images directly to various online services as well as other destinations, for example, social networking sites such as Twitter.
Apple has a list of popular export plugins on its website. You can find it at the following URL: http://www.apple.com/aperture/resources/plugins.html#export.
This doesn't list all of them, however, and is actually pretty backdated. Other popular plugins include some from developers such as Blue Crowbar, which can be found at http://bluecrowbar.com.
And Connected Flow (which provides a Flickr export plugin for Aperture) can be found at http://connectedflow.com/flickrexport/aperture/ ...