I have used same method to collect beta tester for one of my idea. Google adword has given amazing reults so far. Thats why i am interested to know if cost factor the only reason to choose microsoft adcenter over google adwords ?
Does it give more ad impressions for less price + better click through rates?
I actually have better CTR on adCenter compared to AdWords for the same ads on the same keywords (marginally better).
So it's really come down to cost for me. In my experiences it's consistently double or more for the top keywords in the bunch.
I've personally never run a massive campaign to drive tens of thousands of visitors to a site through either service. My guess is, if you need high volume of people quickly, you need AdWords.