Thanks to Kevin S. Brady for pointing this out. And shame on everyone else (including me) for not trying out LinkBunch in Internet Explorer all this while!
The bug would prevent anyone using IE from creating a link bunch. This happened when I changed from the regular, form "Bunch" button to a fancy looking image button. IE sends the image button along with co-ordinates like 'bunch.x' and 'bunch.y' but Firefox continues with a simple 'bunch'. The script looked for the bunch button text and only created the bunch if it was specified, hence it would fail on IE. This was a really stupid but, but it's fixed now!
Also, a minor CSS bug prevented the page from being centered properly in IE. That's also fixed now.