Its true that MSN drives less traffic but if you reach say number 1 or 2 - its still valuable visits for your site
A lot of wikipedia articles seem to be springing up at number 1 in mSN at the moment - even for brand names.
Try this search end study the results: http://search.live.com/results.aspx?q=airline+tickets Pay attention to this "website" http://cheap-airline-tickets.spaces.live.com/ Looks like trackback spam do wonders in MSN
From the last time I checked MSN only produces 7% of all search results. So, even if you rank higher with them it may not amount to much real traffic.