Mixed feelings on the screen protectors.
I say if it's an iPhone, put one on it. Phones go in your pocket, get dropped, get set down in abrasive areas, etc. They take much more of a beating than a tablet. You can basically buy them in bulk on eBay, and that's great because you can keep trying until you get one on there perfectly.
iPad is a little different and that's where I'm torn. You're not going to put an iPad in your pocket and you're probably not going to set it screen down anywhere. I think it's much easier to go protector-less on an iPad without fear. I did it for a long time, but my iPad 2 came from Apple with a scratch already on it, and I eventually used a screen protector to hide the scratch because it bugged me a lot. Eventually I forgot it was even there.
If you tend not to handle your stuff with kid gloves, put a protector on it. My parents have had an iPad 2 for several months now, and I don't have the heart to tell them, but their screen is scratched to hell. It's probably just the coating on the glass that's scratched, but the thing has swirl marks everywhere and it has no screen protector on it. It's probably just from them wiping it down so much because one of them is always using it and it goes wherever they go.
Just my two cents.