I actually installed my Invisible Shield the other day on my ZHD. I had a full body one on my Touch and now just the screen protection on the Zune. I absolutely love both of them, though I did mess up the installation of it on my iPod, leaving a nice finger print in the corner and a crease near the bottom of the screen.
Just make sure you use a lot of the spray and the squeegee, and you should be ok. My ZHD looks awesome and is fully safe now because of it
Also, it does cut down on glare and smudges. It does make the screen less slippery, but I honestly prefer the more tactile feeling of the protector.