Digg, del.icio.us, DotNetKicks, StumbleUpon, Reddit and many other are all social bookmarking sites where users "save online" their bookmarks. So other users can see the bookmarks, and see which are the "hot" pages about a certain topic. Some of these sites also allow users to "vote" for the bookmarks, creating a sort of "popularity contest" where the most voted pages, posts or news should be the most interesting to read.
But all these sites are technology focused (dotnetkicks, digg) or very generic (del.icio.us, StumbleUpon) so it's difficult to find articles about niche topics like climbing.
Or if you are looking for what's happening in the world of climbing and alpinism, but don't want to read 20 different blog or sites, this is a good site to read since it contains almost everything that is happening.
The site started only one month ago, so for the moment not many active users, but hopefully it will grow. They also give 1$ to a "well-known environmental group" per each user that register to the site, so registering will also do good for the planet and for the "outdoor climbing playgrounds".