MSN backend conversions way below average

Anyone else notice this?

[limitup]

We offer a free service at our site. Using the same keywords, ads and landing pages as with Google Adwords, we see a very similar signup converson on the frontend (i.e. users signing up for our free service).

We also track bandend conversions i.e. actions we want users to take, which is how we make money. For some strange reason, on the backend conversions our MSN traffic converts at about 1/10 of what AdWords traffic does.

Anyone else seen this before? Ours is a pretty broad general interest service, and I can't think of any reason this would be the case. But in a nutshell, MSN traffic is worth less to us than Adwords content network traffic, which is very puzzling to us.

Combined with the overall PITA of using MSN AdCenter to begin with, we're very close to just giving up on it...