I had a Zagg on my N900 and it did feel a little rubbery/draggy. Either you get used to it or it wears off, not sure which but the feeling goes away.
I really want to find a screen protecter that is exactly like the ones supplied with the HTC Hermes and Kaiser in the box. Best screen protectors i ever had. Barely even noticed they were there and they lasted the time i had the phones.
Nokia Lumia 800
Retired - Motorola Defy, Nokia N900, O2 Stellar, T-Mobile Vario II