I guess they don't want us to know the site behind of course but there is even a way to do it somehow?
by the way It's just me or all the bids are VERY high lately ? 
Some networks may leak referrers. That's the best you're likely to get.
Even if you do manage to figure out some sort of site identifications, it doesn't matter if you can't optimise by that. The only use I can see for the data is:
a) leaving the blind network to find the placement elswhere
b) negotiating with rep to turn that traffic off, but this is a paradox - if they could do this, they would pass pubids, and if you told them you knew which sites to turn off, you would point out a flaw in their 'blind' nature that they would then want to patch.
sometimes your rep may tell you the placements if you ask nicely.
although you can get a list of inventory from a traffic source another way, but wont let you match pubid's
search your domain or other peoples on wrw. from there it will tell you your traffic sources and placements.
but yeah, the biggest use for this i find is to simply find how deep your banners are in rotation, since a lot of traffic sources dont allow you to see the bid information