Yeah, to a certain extent it's inevitable. Though the interesting thing, IMO, is that for this to happen, you need to be on the web. There are still tons of things out there, like IRC, that predate and/or work around the infrastructure of what we know as The World-Wide Web,
but still use The Internet. If enough people get tired enough of advertising, there are alternatives. But for many people, point & click convenience will be worth it. Besides, this seems like just a small step byond the ads you already see in instant messaging clients.