Was noticing this while playing around with the widgets....
Category cloud gives you many useful options like max # of categories to show, min/max font percentage, and excluding certain categories. The tag cloud however only gives you the option to add a title to the widget. It seems like the customizations in the Category Cloud widget would be in even more use on the Tag Cloud widget.
I'm not using the Tag Cloud widget mainly because I happen to have gone tag crazy and now have a whopping 400+ unique tags which become way too cluttered when using the widget. I am using the category cloud widget however.
The blog I need help with is goofballcommittee.wordpress.com.