I started using screen protectors after pitting the screen of my first Palm pilot. It was ugly! One day I dropped the device - which was not in a case - and broke the screen!

I sent the PDA to 3Com for screen replacement (that cost $100). When it came back, I rushed out and bought a Targus leather case and WriteRights. Since then I've never had a PDA that didn't have a case or screen protector.
I am using an old Palm IIIe WriteRight that was manufactured before they were bought out by Belkin. It has a "gritty" surface that gives a pencil-like feel. I had to cut it to fit, and it's been in use about six months. I stumbled on the package when going through some old books. It was being used as a bookmark for "Handbook for the Palm Organizer."
I've tried using the newer WriteRights, but they don't have the same feel. I've heard good things about BoxWave, and will give them a shot next time I'm in the market for a good screen protector.