The Daily Mashup is a mashup of social, and collaborative software web services.
Popular Photos are pulled using Flickr's web services, it is a representation of their Interestingness in the last 24 hours.
Popular bookmarks are derrived from the social bookmark sites del.icio.us, and furl, additionally populicio.us (which gets info from del.icio.us) is used as well. Links showing up on all three engines
The popular news is from Yahoo! news, most clicked items.
Daily Mashup was created by Pete Freitag, you can read more about him on his blog.