Three great sites spring to mind when thinking about sticky sites for grownups: Stylehive, a social shopping site; Digg.com, a community news site and Daily Kos, a blog / news site for left-leaning people who think about politics a lot. These are not 800-pound gorillas, but they are beloved by the tightly defined communities that visit them regularly.

These sites are sticky because they all solve a big problem with the internet: they allow users to sort through mountains of information (or products, in the case of Stylehive) and use the voice of the community to identify a useful subset.

They are also sticky because of the quality of their content, and because fresh content is served up on a virtually continual basis.

Take Stylehive. This site is addictive for people interested in what products are cool and in sharing their tastes with a wider audience. The platform makes it easy for its community members to create "visual bookmarks" as they search the internet for products. For example, you can easily add products to the Stylehive site using a point-and-click bookmark applet. You can also easily add the site to your own personal bookmarks.

Digg allows users to do just two things: load references to articles or blog entries into the Digg database, and "Digg" articles that have been previously loaded by others. Articles that have been "dugg" more often than others float to the top of the results lists.

As a result, Digg presents the subset of articles that most people find most interesting-- from a list of articles that is far longer than any normal person could hope to process.

Digg is sticky because it is clear and deep, and because the Digg community, through explicitly digging articles, picks the content that is most popular.

Daily Kos heads in the other direction. Rather than simply reflecting the preferences of its readers, Daily Kos has a strong and consistent editorial voice. The political blog / community site's content in the main part of the page is refreshed nearly hourly.

Then there's a significant percentage of the site that is dedicated to diaries, or user-contributed blog entries. These are clearly separated from the primary, well-controlled, editorial content. However, they are regularly referenced in -- and also influence -- the main content.

Like Stylehive and Digg, Daily Kos is sticky because of its high-quality content, the fact that it is always fresh and because it is significantly influenced by the user community.

Daily Kos' successful stickiness lies in the fact that it doesn't rely solely on the voice of the masses to dictate what is interesting. Unlike Digg, which is so mass market that it is often less than useful, Daily Kos's editorial voice helps sort content internally, based on what its editors know of the needs and desires of its readers.

This can be a useful tactic for companies to borrow from, particularly those that know they can't rely on their visitors to take the time to create content or share ideas.