The Live Search Blog announced several updated to their crawler. The first is a name change to reflect the upgrade, previously named msnbot/1.0, it is now named msnbot/1.1.
The bulk of the changes include the HTTP Compression and Conditional Get support.
HTTP compression is supported by many other bots already and is now supported by Microsoft. So for a more efficient crawl, Microsoft now supports gzip and deflate compression methods.
The Conditional Get will aid the crawler in deciding if it should crawl your page again. If you haven't made a change to your page, then crawling the page would not be too efficient. So Microsoft's crawler will include the "If-Modified-Since" header & time of last download in the GET request and when available, the crawler will include the "If-None-Match" header and the ETag value in the GET request. If content has not changed, the web server will respond with a 304 HTTP response.
Forum discussion at WebmasterWorld.