Implementing "Related posts" in CI?

[eluser]aquary[/eluser]
My website was made entirely from CI, including blogs and forums. Right now I select related content manually, which is too boring. So I'm looking for a way to automatically generate "Related posts" somewhere in the sidebar but couldn't figure out how to do it yet.

For blogs, I'm thinking about using tags to determined which blogs are related. But right now I'm storing tags as a single string: "tag1, tag2, tag3", for using it as a page keywords only....

Any ideas are welcome :lol: