As far as I can tell, the launch today is moving their newest technology from techpreview.search.msn.com to beta.search.msn.com. According to Walt Mossberg at the Wall Street Journal, MSN has promised to move their new technology over to the main search box by the end of January. That's less than 2.5 months, so I recommend that everyone spend their full attention coming up to speed on beta.search.msn.com.
It's very rare to get to see a search engine in transition, because that's the best time to see what the different criteria are for ranking.
Do you see their three sliders? They are for "Very popular vs. less popular", "Exact match vs. approximate match", and "static vs. updated recently." It's really cool to play with these sliders. I'm sure that a lot of WebmasterWorld moderators are off tweaking values to get an idea of how things are computed, and what the relative weight are. For example, if you move the slider all the way to very popular and click search again--viagra.com disappears from the first page! That's a little counterintuitive to me, and it makes for some really interesting speculation about what Microsoft means by popular.
Most search engine optimizers will be fascinated by the ability to play with sliders and try to reverse-engineer how Microsoft is ranking. Not since Nutch have people gotten such a good view at the different components in ranking for a major search engine. Because of that and the fact the MSN has promised their new search will go live by January, I'd get busy playing. :)
Here's one other tidbit I came across while reading this morning. Following on Google and Yahoo's launch of blogs, MSN has launched a blog for its search engine as well: [blogs.msdn.com...]
Highly recommended reading--they've got comments enabled, too. I've really enjoyed playing with the new search, and I'd recommend that everyone spend 2-3 days getting familiar with how MSN is ranking pages--I think the effort will pay off.