(As an aside, the PDA thing helped a hell of a lot, which is why I remain reliant on one to this day. People use tools to cover for what they can't do with their bodies alone- well, this tool covers for what my brain can't do.)
Not that I got many more touch-screen devices; I took the PDA to college, but it was rather dated by then, and its battery life wasn't where it needed to be. (And believe me, you care about battery life on a device that loses all its data if the battery goes flat.) So I bought a floor model from Office Depot, bought a pack of "universal screen protectors" (with a 1mm grid on the backing, so I could trim the protector to fit the screen), and went with that for a couple of years, until we switched from Sprint to T-Mobile and I got my first smartphone, the T-Mobile MDA. (I've been with Windows Mobile for a while, yeah.) And it got a screen protector too.
Nintendo asserted up and down that the DS didn't need a screen protector, so I didn't get one. The only scratch it got was when someone ran into my elbow while I was playing Yoshi's Touch & Go, and it was only visible in certain light. But by the DS Lite, they gave up trying to convince people not to use them, so I got a screen protector for it- by now, I was on Invisible Shield. My DSi, in turn, also got one.
So it's almost a heresy that I'm considering peeling it off. But I think screen technology has improved a little bit in the last 14 years. My Nokia N810's been used rather thoroughly by both myself and blackvoiddragon since I got it, and the only damage the screen has taken is fingerprints. The screen protector included with my new HTC Rhodium (or, as T-Mobile called it, the HTC Touch Pro 2) was nearly impossible to apply correctly, looked horrible, and didn't sit on the screen right (it's cut to less than 1/10mm smaller than the screen, making it nearly impossible to line up against the bezel without it leaning up on it on the other edge), so I gave up on it, haven't replaced it, never applied one to Rakeela's, and the screen is absolutely fine. The phone relies on touch so much I can't use my usual screen protector- the texture of the Invisible Shield just doesn't work for that. Actually, that texture is exactly why I'm considering peeling it off my DSi- I don't think it's doing me any good at all.
I see on a lot of mobile device forums threads about screen protectors, with the occasional person mentioning not using them (generally for screen texture reasons, same as mine), and not having particular trouble with scratches. They're usually quiet voices, and don't divert the conversation much, but I think they're right: screen protectors are outmoded, unless you like to shove your electronic devices in the same pocket as your car keys.
So having used my (kick-ass) new phone for a while, and using it rather aggressively, and discovering that it looks quite literally like it's been completely unused after a quick wipe with an optical microfiber cloth- I really don't think screen protectors are needed anymore. I'm going to stop advocating them, at least.
*peels InvisibleShield off DSi*
Edited to add: ...wow, I hadn't realized just how non-invisible the InvisibleShield was for reasons other than my own imperfect application. Seriously yellowed. I should probably scan it to show the yellowing problem I've heard rants about.