WhosTalking was referred by a comment to a posting here on EverythingTwitter. It scouts across social networks looking for posts around whatever search term you include. The site searches across a reported 60 social sites (which sites it searches was found later) and uses and AJAX interface.
When the results are returned, the middle is a descending, combined timeline of items it finds across the networks. All are hotlinks to the direct sites themselves. It would be nice if they could provide some preview when hovering or clicking before opening new tabs/windows.
The left column allows you to sort by a myriad of options and sub-options:
These suboptions show the individual networks that are searched for further filtering. Below that was a hidden feature of options. It allows you to save the search and even get an RSS feed result of your search to follow in your favorite feedreader.
Why was this important to Twitter? Well it is really a search tool but shows the topic across sites, possibly growing the conversation just found on Twitter.