a tip on exchanging links
This story is old (from 2000), but the lesson I hope is still useful.
Years ago a certain link exchange service who shall remain nameless was bought by a certain company.
Once that buy-out happened, the number of my banner ads sent to other sites through the service dropped to less than a quarter of the number of ads I was serving for them. Upon writing them, I was told "don't worry, we promise a 1:1 return on the ads you serve, so you will get them all in time". Well, that didn't happen before I switched to BurstMedia who I was very happy with.
I suggest keeping very close tabs on which ever ad exchange service you choose and make sure they keep to their promised ratio. I think it would be impossible for them to catch-up if they fall behind in the number of your banners they promise to serve.
(sorry for the run-on sentences)