I have replaced the skinnier tires on my touring bicycle with Marathon plus, 700c x 38 tires. They are much more comfortable and supposedly puncture proof! So good so far.
Since putting them on the bicycle, I have cycled on pavement, grass, dirt, wet pavement, horse poop, wet leaves, muddy pavement, crushed gravel, wet crushed gravel, cobblestones and brick in a variety of patterns. The tires work all well on all these surfaces and situations.
I was worried that fatter tires would be slow but I don't notice a difference. Maybe, because I'm slow anyways... however, I do feel more secure going over bumps and rickety brick work at pace. The vibrations do not jolt me as much as before, and my hands are much more comfortable.
I installed the tires myself. A few online forums indicated that they would be hard to install, but I had no problems. It was good practice to remove my wheels and put them back on the bicycle with only the tools that I carry when I ride!
My only issue now is that the height (not width) of the tires has made it impossible to keep on the front fender. My back fender is fine, but there isn't enough clearance between the tire and the fork. I bought a downtube mud guard but it didn't really help during a massive rainstorm.
But then again, I'm not sure a fender would have helped much either. Rain! Rain! Rain!