Everything works with the exception that the upload queue never appears. I tracked it down to a silent crash in the uploadifySelect bind and managed to fix it (twas an unscoped variable).
In the unminified v2.1.0 js, line 122:
queue = '#' + jQuery(this).attr('id') + 'Queue';
Becomes:
var queue = '#' + jQuery(this).attr('id') + 'Queue';
I've not confirmed the bug in other versions of IE but it does not manifest itself in FF 3.0.