MSN Beta is still serving up results that make any SEO jump for joy. It is very easy for many SEOs to rank well in the new Beta Search engine by MSN. A thread at SEO Chat asks the question, How long will MSN SEO Heaven Last?.
To address the question, I personally do not know. I would think for them to become a serious engine that competes (in terms of relevancy) with Google, Yahoo and Teoma on relevancy, they will need to make some major changes. This doesn't necessarily need to be the day they go live, but as soon as they want to compete in terms of relevancy.
I am not a fan of theories but I thought I mention a theory in the thread. Jasontnyc, one of the newest moderators at SEO Chat feels that MSN is offering results that the SEO's want to see. His reasoning is that most normal users have no idea that MSN has a beta engine, but most SEOs do know this fact. By providing results that are attractive to the SEO community, MSN can start a nice little marketing frenzy amongst the SEO community. This marketing tactic might dribble down to those in the mass search market.
I have noticed Yahoo! especially, and Google appeasing the SEO industry more and more these days. The public relations departments at these companies are aware of the SEM industry and might see it as an avenue to do some grassroots promotion.