Crowdsourcing is to Web 2.0 (the human web) what Outsourcing was to Web 1.0 (the corporate web).
Web 1.0 allowed companies to outsource white-collar jobs to India. Now Web 2.0 allows marketers to hand their work over to Amateurs - and the results are faster, cheaper and more effective!
Traditional brand marketers may be dismayed at what the public would do with their message, but the rewards for those who've relinquished control is wildfire word-of-mouth buzz and sales.
Google Trends graph (reflects internet buzz) - S.o.a.P. vs. Pirates of the Carribean
More reading: Networks Unbound