As Stack Overflow has grown, it has become increasingly clear that we're going to have a significant amount of unsold ad inventory for the forseeable future.
And the open source advertisement idea is a good idea to do something about that.
I just had another one: Give developers who filed their CV on careers.stackoverflow the chance to create an advertisement to be put on SO, maybe next to questions / answers they have posted, or maybe in relevant tags. This should be cheaper than regular ads (maybe even free? At least for early adopters?) and should link exclusively to their CV.
Of course the ad would be subject to review as they all are (no "<span style='font-size: really-huge'><blink>Hire ME!!!</blink></span>"), but it might be an interesting extra feature for devs who really want that great job they dream of.
What do you think?