I've long noticed that the most popular pictures on Smugmug tend to come from the Daily Photo community. Do the photos which show up on the top actually result in sales, or is it more of just method of attracting viewers to one's site?
Can't say increased sales (no way to really know that) but I can tell you that the Daily Photos community does have a pretty high viewership, since they are 1) good photos for the most part and 2) there's lots of activity (comments, thumbs). These show up in SmugMug's Daily popular photos on the browse page. Being involved in a community is a great way to get more folks visiting your SmugMug site. Combine that with blogging, posting on forums and other communities, posting on Facebook, Google+, Twitter and you can see a big increase in viewership - which, for many types of photographers, can mean more sales.