Paulo Coelho has found that putting his own books online as free EBook files has increased his print sales.
Update: now Harper Collins is putting up some of his stuff for free. Brian Murray, president of Harper Collins, said that the free electronic editions would be available only for one month, and readers would not be able to download them to laptops or to an electronic reader like Kindle from Amazon.com. The print function will also be disabled, but readers will be able to link to retailers like Amazon.com to buy copies of the books.
Apr29 update: Scott Sigler has used free Pod Cast versions of his book to promote himself.