For the little bit the SaaS has been up, people still seem to like the self-hosted version. So, I guess it really depends upon the product and your target customer. There's some things that some people just prefer to host on their own :-).
Do you think maybe it's a self-selected audience? Like these are the people that know and love you as a self-hosted product, and now you need to reach a different, more SaaSy crowd?
I've had many people coming from OpenX that found OpenX too cumbersome, slow, and/or confusing. So, it's a different customer base - they don't need the millions of bells and whistles, just want some quick and simple to use.
I chose it because people in a forum I was a member of were asking for such a thing and thus I was presented an opportunity.
For the little bit the SaaS has been up, people still seem to like the self-hosted version. So, I guess it really depends upon the product and your target customer. There's some things that some people just prefer to host on their own :-).