It's rumored that in the coming weeks Microsoft will launch a deep site crawler. Up to this point, MSN indexes pages frequently, but doesn't dig out and index all the pages of a site like Google. Deep crawl is an SEO term that means the bot indexes pages several levels deep and in the case of URLs with multiple query string parameters.
This should have a significant impact to large sites and to the SEO community. I'd expect to see the number of pages indexed in MSN from a site grow rapidly. Lots of people have been clamoring for a real competitor to Google. I think this is a great step for MSN for two reasons. I suspect the quality of the results will increase since more content from sites will be included and I suspect it will be even more impactful on the SEO community. Sites that are large with good content should see a pick up in referals from MSN.
These are big changes and its great to see MSN getting this out there with Ad Center, and the froogle competitor.