CTR and landing page relevancy are factors, similar to G. The exact formula, like G's, isn't published.

What sort of landing page relevacy? Are they as strict as google?
How long does it take high CTR to lower your click costs if you are a new advertiser on a keyword?

What sort of landing page relevacy?
If what's in the ad and keyword are aligned with what's on the landing page.

Are they as strict as google?
I think you're confusing land page relevancy and page/site quality scoring components that G recently added. On relevancy, they are nearly similar to G in my experience.

How long does it take high CTR to lower your click costs if you are a new advertiser on a keyword?
From what I have seen, it is much faster than G, but still depends on how fast you are getting clicks.

I have been noticing that MSN price per click varies wildly during the day, and so does position. Don't they weight past click history? It almost seems like they determine CTR hourly, or daily with no regard to history. Or is it that it takes several weeks to have that history, and thats why things are volatile...

I think it's because they're are fewer bidders, so as things dynamically adjust, the increments between people are larger.

And MSN has dayparting and incremental bidding that can add more variables.

And since there's a lot less traffic than G, you're looking at fewer data points and comaring them to the same time slices at G (hourly, daily, etc) and less data generally means more apparent scatter.

In any case, the ROI's been very good for me, so the lesser "behaving" stats that seems to be there, hasn't been a concern for me.