Just ran across TwitterJobSearch.com yesterday and thought it was a great tool to share. With a very simple interface (much like Google), TwitterJobSearch.com aggregates all Tweets pertaining to job listings and allows you to search for them. For instance, if you wanted to find jobs in Minneapolis, simply type "Minneapolis" and a list of all the job Tweets in Minneapolis, MN will appear.
If you are in the search for a job I would recommend setting up some RSS Feeds of the jobs you are interested in. Type in the term(s) you are interested in and then click the "Subscribe" button on the page. Now every time the search engine finds a Tweet with your term in it, you will be immediately informed and will be able to react quickly to opportunities.