I'd put $1 on the following proposition: 30 years from now, the advertising industry (i.e. in which sellers of products pay directly for advertising - advertising which is not content and does not attempt to confuse the receiver about this) will have less than 1/10th the revenue it does today, as a proportion of the total revenue of all industries put together (I'd say "GDP" but I think that may be defined in terms of profit rather than revenue - and I expect margins to shrink everywhere).

(I think we'll see a big rise in viral marketing, shill and semi-shill reviewing (Klout, amazon's programme where they send products to highly rated reviewers), product placement and sponsored content (the my little pony cartoons; mad men with jack daniels; akb0048), which will blur the line between advertising and content creation. But I think outright ads will collapse)