Have one on since the minute after my L900 came out of the box. Maybe it does dim the screen a little, but with my failing eyesight I don't notice it. Brightness is always set to Automatic.
What I do notice though is the way my fingers glide over the non-slippery surface of the screen. And, the fact that I have wiped this screen exactly two times with a microfiber cloth since 4/6/12. And looking at it right now, not a single fingerprint. Oh, and my phone is awake and in use at least 4-5 hours every day. On my Surround, with an AT&T branded screen protector, I had to wipe the screen several times every day, and wash it a few times a week. This protector is like magic.
I expect it to be around as long as I own this phone.
Sent from my Lumia 900 using Board Express