I use tags on my blog for years. First it was done with UTW and when WordPress MU 1.3 got released I switched to native WP tags.
The first thing which I missed was nice Tag Cloud widget. Default WP one just printed all tags without giving any control to user about how it have to look. So I looked at source and wrote own version.
How to use it?
Fetch archive, unpack into
wp-content/plugins/ directory and enable “Hrw Tag cloud widget” in “Plugins list”. Then go to “Presentation/Widgets” and replace “Tag cloud” widget with mine. You will see configuration options.