As far as iPhone covers go - I have the silicone one with the hard plastic flip-cover for the screen protection. I have seldom used it for these reasons:
1) the phone's ringing volume has always been a problem and a cover makes it worse
2) have to uncover it to dock it for charging, which is something I do every time I get home - it's a habit because I often forget to charge my phone
3) the flip cover makes tapping on the screen an issue, have to flip the thing up and down all the time
4) one of the attractions of the phone to me is it's slim feel, any cover makes it bulkier and spoils it for me
I've managed to keep my phone fairly safe (touch wood), not a scratch other than on the chrome rim around the front panel, little hairline scratches there. I've had my phone since Dec 2007. It's a bit slippery in a pocket, but at the same time, using silicone makes it difficult to retrieve, so not sure if I would suggest a cover for anyone.