I've added a simple "tag cloud" showing frequency of the top 30 searches in iSpecies. It's a bit ugly, but you get the idea. You see the tag cloud if you go to iSpecies directly (i.e., no search term).
I made use of a nice article on scaling tag clouds by Anders Pearson. He describes a simple function to scale the tags. I put this into an Excel spreadsheet as a quick hack (in other words, the tag cloud isn't dynamic yet).