It's one of those domains that sounds great but when you look into it, then it's not. Online advertising is obviously a big industry, and will only continue to grow, but I think most firms offering this service would use a brand rather than a generic.
It would be a perfect domain for an information portal. I think that kind of buyer isn't likely to spend a lot on a domain - more of a "webmaster" level price rather than end user price. I'd still aim for mid-$xxx on it though for any unsolicited enquiries.