People use us over Bitly because they earn rewards. What we know from the feedback we've received is users don't like seeing blatant ads (ex. banners) on the page. Our response has been to syndicate other content the user has shared; so far the design has received a some praise and nobody has complained (whereas w/ ads we received complaints), but the change hasn't been live for long (less than a month ago we were showing ads).
The money in a publisher deal flows opposite of the direction you described. They would pay us to get their content syndicated on the interstitial. From my limited knowledge, ad sales for bigger publishers start from 10k and go up, which means we need to guarantee (at $1 CPM) 10M impressions. Currently the service does about 3M monthly impressions, so we're not quite there yet.