The only thing bad about MSN is the amount of traffic.. other than that, they are better than adwords in every department.... but if you have like 200 keywords of a widely searched niche, you dont feel the difference... And really, its not the amount of traffic that matters.. its the quality.. you do PPC to make money, not to improve your traffic stats.. for that, buy loads of junk traffic....... Moreover, vouchers for msn are easier to get..... A bad thing, vccs dont work with adcenter... no matter how new your BIN is..... Ohh and the AJAX system is a pain in the ass if your internet connection sucks......
Still, you can use Google keyword tool to generate high traffic keywords on Google, and then use the same high traffic keywords on MSN, bid higher and you can possition yourself as first in the results page. I'm sure if you will target keywords like "Free Games" ,etc. you will see your voucher amount getting vanished before you notice.