You might have seen the tag clouds posted below. I calculate tag positions based on co-occurrence, such that tags used together are placed closer to each other. Additionally, tags are scaled áccording to frequency.
A general problem I have with the resulting representation (and common tag clouds as well) is the fact, that every tag occurrence is weighted equally. As a result, these tag clouds never represent the current state of interest, but a very sluggishly changing summary of your archive. However, your interests and the corresponding vocabulary keeps moving on. So I am currently investigating trends in tag clouds and how groups of related tags emerge and disappear again.