Automated tag cloud widget for forum content?

I understand there's a tags widget, but I'm not sure if that can be used for my intent. 

I'm trying to configure a tag cloud that will pull in common/hot keywords used throughout forum posts automatically. E.g., if "programming" is used a lot, then that keyword will display in a large font without having to re-categorize each piece of content. 

Does something like this exist? Can I use the tag widget out of the box and accomplish this with configuration, or will this be custom? thanks.

Have you tried this post.

www.sitefinity.com/.../tag-cloud-on-blog

This isn't automated, is it? It doesn't appear to be. Also, I would need this to work with forum posts, not blog posts, and I don't believe (even if it wasn't automated) that I can tag forum posts with tags.