I've had two sets of Marathons, currently have the Pluses. They have been bomb-proof. Great tires. It's true they weigh more than other tires, but I have them on a touring bike that normally weighs in around 90 pounds when completely loaded up. I want tires that can take some abuse and not flat a lot. I hate dealing with flats on a loaded bike. They've been on my bike for about a year now with two tours on them and zero flats. Still have lots of tread on them. I don't notice any difference in rolling resistance over the previous Marathons (HS 420, I believe). That said, if you're riding a light bike and worried about ounces, go with something else.

Edit: Mine are 26" x 1.75"