I took it out! I couldn't get the 'wipe the coating off' method to work and tried several different fluids. I would try it with the IR filter lens in place and if it does work fine with IR LED's (as everyone seems to report), you can use the cam for headtracking and as normal. If you do remove it, then the focuss will be slightly off (which is ok for headtracking). The case is a bit of a pig to separate and needs a bit of 'persuading' even though there are no screws holding it in place.......
I used the 'floppy disk' film suggestion to cover the lens (or fit inside the cam as most vids describe). It's all fairly straightforward and tons of info on the net/Youtube etc.