ive used glass tops for years! i will never take them off.
Pros: easy to clean salt creep, never have to be replaced, cut WAY down on evaporation, keep fish from jumping out, plus, they look good and protect your lights. you wouldnt want water to splash your lights would you?
Cons:less gas exchange so im told (i have no problems), raises temp (i have halides and a heater and my temp is a comfortable 81 degrees), less light (once again i have halides and vho's, even without the halides i really dont see much of a difference)
i thought about egg crate, but water can still splash, im afraid of it melting, and water will evaporate very quickly. plus, its just plain ugly on a tank.
so, i will never get rid of mine. i left them off for a couple days, and my water level went down an inch a day! WAY too much water for me to keep up with topoffs, plus i have to buy it. i just do a weekly biweekly water change and i am fine.