I just went into my AdCenter account for the first time in months.
What can I say?
Volume is so low in comparison to AdWords that it's a joke.
I revised all my keywords to adjust bids but mostly they indicate that I show up 1 or 2 without any changes.
With the same keywords I spend up to $1000 per month with AdWords. My bill last month from from MS was $13.00.
Not worth the time or trouble unless some major changes occur.