I did something very similar in the past except I used Cosine Similarity (http://en.wikipedia.org/wiki/Cosine_similarity http://en.wikipedia.org/wiki/Cosine_sim

I did something very similar in the past except I used Cosine Similarity (http://en.wikipedia.org/wiki/Cosine_similarity http://en.wikipedia.org/wiki/Cosine_similarity). It allowed me to give each tag a "weight" and when comparing the tag clouds, I would zero out any that aren't found. It works really really well.