I love the look and feel of the WP-Cumulus tag sphere, but I experience the same problem as another user a few months back; since the sphere is tied to the WP-generated tag cloud, it shows little rotation of different tags.
It would be nice if the tags displayed in Cumulus could be (optionally) randomised, so as to display a customisable number of random tags, which are renewed on each page load. If that would be possible, I could use the tag sphere as great way to encourage visitors of my site to discover older posts on a random basis.
Evening of Light
P.S. We now use a random tag cloud plugin widget which has the same functionality, but a more basic look.