I'll try to get more information after the official launch. FlipDog looks like it's acting as a specialty search engine, scraping employer's sites for job postings and making them available in a massive database. At the moment it looks like they've got over 200,000 listings in their database right now. The big thing about this is that FlipDog isn't charging anybody to list the jobs, like other big job sites do. That's good for them in that it's going to allow them to create a huge database.
Employers do have the opportunity to opt out.
Picking a city and watching the number narrow down is kind of cool. This looks to me like a perfect opportunity to use the RSS syndication model. Still, anyway, it's worth a look. On a single page you'll get explanations and forms for search engines, meta-search engines, categorized links, collections of site reviews, and more. An excellent introduction for a beginner or a refresher course for a more advanced searcher who's wondering if there are any tricks they missed.