Zach put it. He has a point. I think the tag cloud is probably the worst idea in the history of the internets. “why not put all the tags we have, and shove them in all together!” Tag clouds are often mistaken for visual eye candy. Please avoid them. Seeing hundreds of text links is painful to the eyes, and provides no useful information whatsoever.
The conclusion of my rant is this. Tags are a very nice idea, but only theoretically. The technology is flawed because it places full control in the hands of the users, who more often then not prove themselves quite incapable of using it properly. Moderation of the tags is needed before they can be used effectively in any web application.