Microsoft adcenter have a good and quality traffic, but they are also going against affiliates and your ads may get rejected most of the time, but they have very good support team that can help you go over that. Make sure to see their PPC training here : http://advertising.microsoft.com/support-center/training-accreditation Good luck
Microsoft adCenter is a collection of tools and information that you can use to place advertisements for your business on the Web. Ads that you create with adCenter can appear on Live Search results pages, or on MSN-affiliated websites with related content.
Adcenter used to be easy and much more laid back then Adwords. Now they are tightening up like Adwords. If they dont like your page or whatever you're promoting they will stop sending you traffic and say nothing to you. Only after calling in several times and waiting on hold do they tell you "Oh yeah, after speaking with the quality assurance team (which by the way is some top secret group of employees in a dark room somewhere with no phones) your website just doesnt fit the bill for our program" Long story short, you have to open a new account with a new credit card and business name everytime this happens if you want traffic from them.