The race is to provide a way for email users (and isn't that just about everybody?) to efficiently and effectively search their email. Outlook doesn't do it well, though there are improvements in the 2003 version; so third-parties are having a go at it, including Google who is beta-testing an web-based email product with Google search functionality, Gmail.
Another email search company, X1, is partnering with Newsgator to provide search access to Outlook email AND Newsgator RSS files. This news item, NewsGator, X1 Push RSS-Search Connection, is very interesting in more ways than one.
Note this quote from Robert Scoble, technology evangelist at Microsoft, "NewsGator is the best RSS aggregator out there, especially if you use Outlook on a daily basis. Likewise, if you use Outlook, X1 is the fastest and most powerful method of finding and using all of your various data -- a little bit of Longhorn for you before it ships," Scoble said.
In addition, Bill Gates has been busy explaining RSS to CEO's, and does a nice job of comparing the advantages of RSS over email for certain kinds of communications.
So is a buyout of Newsgator in Microsoft's future? Greg Reinacker, the president of Newsgator, says he certainly considers Microsoft a partner, but would not comment beyond that. Either way, RSS is obviously going to play a role in the next version of Windows, which should bring RSS into the enterprise and the mainstream.
The HotBot desktop searches and indexes outlook express. I haven't used it that much so I can't vouch for this feature but Greg Sherman has a good article at http://searchenginewatch.com/searchday/article.php/3339921