I wanted to say more about viral sites. I think there are two really cool features that can be implemented to improve your SEO and also utilize the Blogosphere more.

Widgets – get people linking to you
Offering widgets makes it very easy to get people to link to you. For example, I could create a widget for Best Seattle Bars that allowed people to drop some code on their site and display a list of the best Seattle bars. I could also create a widget for Best Seattle Bars that allowed people to drop some code on their site to display a search box. The two best advantages of using widgets are 1) you get people to link to your site, which improves SEO and also increases referrals, and 2) you get to control the way that people link to your site. Here are two examples of widgets that Trulia, a Redfin competitor, offers:

Pretty nifty, huh?

Trackbacks – encourage bloggers to link to you
Bloggers love to blog. If you have rich content on your site such as homes for sale, restaurant reviews, or travel tips, then chances are good that bloggers are already blogging about you and linking to home, restaurant, and travel pages. Reward them and maybe they’ll blog about you more. Setup a mechanism on your site to capture trackbacks sent by blogs, and put a link on the page that’s being linked to, linking back to the blog post. On Best Seattle Bars, an example would be to put a link to each blog post that links to a particular bar page at the bottom of that bar page. You would probably want the link to be nofollow, but bloggers would still get referrals from these links.

The largest factor of PageRank is link analysis, so the more people that link to you, the better you’ll perform in search engines.  The better you perform in search engines, the more people you’ll get coming to your site.