My client loved the functionality so much (especially the div popups when the user hovers over different days in the calendar) that they purchased a suite of licenses for it. Problem is that it is not particularly clear from the Bamboo Solutions website how to register their web parts after you've purchased a license.
The List Rollup Web Part is installed in the GAC, so it shows up in the Windows Application called the "Bamboo License Manager" in a drop down - however, turns out that the calendar web parts are installed to physical locations (ie in the bin directory of your Site Collection) rather than the GAC. Consequently, they won't ever show up in this dropdown.
It seems odd that the install methods are inconsistent, but the controls work well so I'm not going to complain. Consequently, you will have to browse each of your site collection physical locations (e.g. c:\inetpub\wwwroot\wss\Virtual Directories\PORTNUMBER) and activate your license for each individual site collection you use your mini-calendar or other web part control.
Now you can just do an iisreset at a command prompt and your Bamboo web part is now fully activated!