I know that in order to get a good search engine page rank the last thing you will want to do is join some dodgy link farm website. However, does the same apply for websites such as Reddit, Digg and StumbleUpon? Do search engines look upon them in the same light?
The difference between Reddit, Digg and other bookmarking sites is that your link will only be displayed for a few days. After this it will become buried underneath all the fresh links. This is why websites published on Digg are usually indexed within a short amount of time. Link farms on the other hand are a bit like pyramid schemes.