Just out on their blog a few hours after the Microsoft announcement:
“Given this new type of information and its value to search, we are very excited to announce that we have reached an agreement with Twitter to include their updates in our search results. We believe that our search results and user experience will greatly benefit from the inclusion of this up-to-the-minute data, and we look forward to having a product that showcases how tweets can make search better in the coming months. That way, the next time you search for something that can be aided by a real-time observation, say, snow conditions at your favorite ski resort, you’ll find tweets from other users who are there and sharing the latest and greatest information.”
Interestingly, with two large partnerships in place this probably proves that Twitter are in it for the long haul and won't be selling anytime soon!