IPhone screeb protector residue?

I have personally never had that problem with screen protectors. I would try rubbing alcohol (not a lot, put a little on a paper towel or rag). Or if you have a first aid kit around get an alcohol wipe (or whatever they are called).
I would also recommend against whichever brand of screen protectors you are currently using.

Will you please fill us in on what screen protector you are using so we don't follow suit?

The only thing that should ever be used to clean your screen is a soft, slightly damp, lint-free cloth. If it's a 3gs, the cloth should not be damp. Damp means water, you should never use window cleaners, household cleaners, aerosol sprays, solvents, ALCOHOL!!!, ammonia, or abrasives.

A little alcohol on a cloth won't hurt at all. It's much better/safer than using water.

Not according to Apple:

"To clean iPhone, unplug all cables and turn off iPhone (press and hold the Sleep/ Wake button, then slide the onscreen slider). Then use a soft, slightly damp, lint-free cloth. Avoid getting moisture in openings. Don’t use window cleaners, household cleaners, aerosol sprays, solvents, alcohol, ammonia, or abrasives to clean iPhone. If your iPhone has an oleophobic coating on the screen (iPhone 3GS only), simply wipe your iPhone’s screen with a soft, lint-free cloth to remove oil left by your hands and face."

http://www.apple.com/iphone/how-to/index.html#basics.cleaning-iphone

Apple has to write their warnings for the lowest common denominator. While I wouldn't wipe the plastic back with an alcohol soaked rag, I will continue to clean the glass on my 3G with a bit of alcohol on a soft cloth. Again, alcohol is more safe for the electronics than water - it evaporates and is much less likely to leave residue. Carefully used and it's OK.

wjosten, if my post immediately above came out a bit curt, sorry, it wasn't meant to be.

Wasn't taken that way, in fact I agree with you. But, I think here it's best to stick with "official" recommendations if ya know what I mean 🙂.

You need to be careful here... try something like goo gone or another citrus based cleaner... use sparingly and keep on the glass only. Placing another screen protector without cleaning the glass is a waste of time.