Ad-washing software: At least three companies are running around peddling software that removes ads from Web pages as they're being served. This has been tried before in other media, specifically television, with no success. But if it were to gain traction on the Web it would further frighten already skittish advertisers.
Continued softness in advertising, particularly TV: As long as the economy continues to wallow, ad revenues are likely to remain flat. Or down. And television's softness (network and cable CPMs down by as much as 15% versus last year) means that all other media suffer even more.
Advertising effectiveness: Despite several recent studies demonstrating banners are good branding tools, marketers are skeptical. After all, they ask, how many banners can YOU recall? How can something so teeny be memorable? Just one bit of research showing Web ad INeffectiveness would get wide play in other media.
Content police: Why are some politicians all upset about content on television, movies, and music when eight-year-olds can easily get graphic lessons in gynecology on the Web? It's only a matter of time before some government entity will begin doing some serious prowling around this freest of media.
Consolidation: Almost every day sites disappear or are gobbled up by bigger ones. Continued consolidation of ad-supported websites would turn this medium into another network cable TV: lack of choice for the consumer, lack of negotiating leverage for the media buyer.
Sales tax: States are gradually waking up and charging sales tax on Web purchases - but only if the consumer and retailer are in the same state. That's one gigantic loophole that could be closed by simple cooperation among the states, and one of the Web's great retail attractions would vanish.
Screen-grabbing ad formats: Marketers are understandably uncomfortable paying for ads that don't fully load onto the consumer's screen. There are technologies that effectively freeze the screen until the ad has loaded and run - good for advertisers, terrible for the Web.
Death of Amazon: There are those that believe that the demise of Amazon, whether by bankruptcy or acquisition, would be 'the other shoe dropping,' marking the REAL bottom of the market. Others say it would mean the death of online retail.
Truth in spending: Like Fermat's Last Theorem, accurate accounting of ad spending on the Web has proven to be an elusive goal. Until there are good numbers available to advertisers-such as exist for virtually all other media - the Web will be looked at with suspicion.