Pretty much everything about "pushers" has been summed up in this thread but the one thing I would add is that developing a really good drop shot is key to beating pushers. As someone else said, draw them into the net and then fire a few at them or lob them as they do to you. You really do have to finish a good amount of points off at the net or you'll be playing all day long.
There's a guy who I play occasionally who is a really good pusher. He ends up beating a lot of guys who are better then him just by using typical pusher techniques. He only plays local guys, mostly undeveloped players so he thinks he's great. He gets really mad if you tell him he's a pusher and says how he beats everyone so how could he be that bad? I mean this guy must shank 40% of his shots but they all end up over the net. I need to videotape this guy because he's really gotten fantastic at pushing. Personally, I just don't enjoy or have fun playing guys like that so I don't. I actually think it might be worse for my game since I'm slowing down my reflexes so much that when I hit with someone good I'm late on the ball.