There is an good thread at Cre8asite Forums discussing the effects of doing search engine optimization on one page websites. Most of us know these sites, generally they always try to sell you on something. Whether it be collecting information, clicking on Adsense, or trying to get you to visit somewhere else these sites can be useful to the marketer but they can also have their limitations. The thread starter asks, "How would this affect one's SEO strategies? Is it more of a benefit to having one page whereby you are scrunching all of your content, and subsequently, your keywords onto one page?"
Ammon posts some thoughts on the subject:
A one-page website always has less options than a multi-page website. That always means it has limitations, and is slightly handicapped (possibly a lot more than just slightly).
Your own internal links and link text (navigation) have weight in many search algorithms. Your site structure can have weight. With a one-page site there are neither internal links, nor structure.
Whatever you can do to make one page successful, you could do to six pages to make the site more than six times as successful.
Continued discussion at Cre8asite Forums - One Page SEO