Although my results are the opposite of most here I think there is a 'magic number' with Y. Be careful if you are handling alot of weight.
I don't know about this. I had Yahoo pick up a news article that I fed through the co-op that just about every AP writer and their grandmother wrote about when the news came out. I happened to get a little bit of a scoop since I got the news from one of the sites that first reported it. Co-op ad went up almost immediately and I ended up with the top yahoo position for a highly relavent search which I still hold on-to (even though I've greatly reduced the weight associated with the ad). It brought me a huge adsense burst in revenue (20x my normal daily puny numbers) for a week, tripled my site traffic, and was by far my most popular page for a month. It's been a while, so it's tapered off. I also noticed several click-throughs (much larger than normal) for the ad from the network itself. I don't know if the ad network helped me gain the top position in Yahoo or if it was just the timing of the yahoo crawl and the posting of the news. I've used the strategy twice more with varying results - one it performed just as well, but the news was not really that intriguing so the volume just wasn't there, and the other was a story that many others had been tracking for a while and had background articles up for which I did not. That one I never did get any ranking for.