It's because it thinks the function gotoCompose isn't there. It's commented out, ish (yes in IE, no in everything else?), using <!-- --> in a jQuery function just under #posts div.
That's my guess at least. If that's it, there's nothing you can do, it's a bug. I dislike IE loads, too, especially wrt to styling and not keeping up with css3 things but it's getting better. And with all the other devices available, I now hate other things more (mobiles, all flavours).
I mean, I hate developing for them. I like using them.
Sorry folks are feeling left high and dry - that's obviously he opposite of what we want. Afraid we don't know the precise techy details of why stuff isn't working in IE, but will consult with the mighty tech and try and get some answers for you