I've opened mine to dust and to focus the lenses. The dusting is quite simple. I think you just need to remove the top shelf as well as all the screws on the back that have an arrow ==> pointing at them.
Keep in mind that the TV can hold a charge even after it's unplugged, so make sure not to touch anything other than the lenses when you open it up. I just used a soft glass cleaning cloth to gently wipe the dust off the top of each lens.
Last time I did this was about 3.5 years ago, so it's a little fuzzy. The set is now sitting in my garage. Haven't got around to selling it yet. (Currently using a Samsung HL-67A750 67" DLP)