That could be a key. Fastclick is pretty popular among sites "not good enough to qualify for google". Which is pretty much all the second tier sites. It is pretty much the first choice of the second tier so if they are bundling the power of that(and this is the key phrase) advertising competition to take on GOOG it could cut into ad revenue.
Another sleeper is Bpath. They claim to have their banners on 20% of all webpages worldwide. They just recently launched their bidvertiser business, and idea they obviously got from GOOG. You can see that in the bottom left hand corner of their home page
Interesting. I think we've all seen their ads, but I wasn't aware of the leg up they seem to have on targeting audience. In all honesty, I'll be surprised if they themselves become a big thorn in Google's side . . . but it's an example of the kind of technology that Microsoft will thrive at copying and improving -- with the might of their software developing capacity.