Tag clouds are an interesting visualization technique because, unlike bar charts, you can easily display 30 or 50 weights in a compact figure. Moreover, because they are a 2D structure, you can more easily cluster similar tags together. The Tag-Cloud Drawing problem is the optimization of the layout of the tag clouds. It is somewhat related to the Graph Drawing problem.
Recently, Fujimura et al. showed how to scale tag clouds further… up to 5,000 attributes!
We use a topographical image that helps users to grasp the relationship among tags intuitively as a background to the tag clouds. We apply this interface to a blog navigation system and show that the proposed method enables users to find the desired tags easily even if the tag clouds are very large, 5,000 and above tags. Our approach is also effective for understanding the overall structure of a large amount of tagged documents.
I really think that tag-cloud drawing is a topic deserving of more attention. It is both a fun and practical problem.