I implemented themeswitcher so I could style the plupload control.
When I tested my SSL site in IE8 I got the mixed content warning although fiddler and temporary internet files folder showed no "insecure" content :))
When I tested in compatibility mode the mixed content warning and themeswitcher disappeared ....
When I tested in IE in http mode the themeswitcher control is there but it does not style the plupload control although FF, Safari & Chrome do.
I have written code to test for IE and I do not load themeswitcher if that is the case.
It is unfortunate as it seems to work on the plupload demo but it took me so much time to implement it in SSL and to get all the thumbnails for the dropdown local and to change all paths in themeswitcher.js that I am pretty spent and will wait till IE9 comes out to retest and activate for that version and up if that is the case.