I have been using an IS since I got the phone and am glad I went with it. It's a nine piece set, including one for the lens cover surface where it reads "Carl Zeiss"

I'm not going to talk about all the normal stuff to expect when using any IS or any other similar shield, you know the issues and can expect them across the board with every option.

The only thing really worth mentioning, is that it does change the behavior of the resistive touch screen. It takes just a tad bit more effort when scrolling for example, compared to without something covering the screen. It's not that big of a deal, but to all those sad souls who might have the Apple marketing nagging them from the back of the head, it's worth mentioning as an unbiased opinion.

Aside from that, the protection of the touch screen with a shield easily outweighs the .00000001 additional force required to operate the screen!