Regarding mulching, as long as you keep the bottom cleaned out, you shouldn't have any problems with it. A lot of times when you're mulching tall or wet grass for example, it can clog and build up on the bottom of the deck a lot easier and faster than if you're bagging it. This build up can cause the engine to bog down which of course is hard on the machine and is why you'd then shut it off, and clean out the bottom. A lot of people will keep on running the machine when it's bogging down which you could arguably say, wears the machine out quicker and lessens it's life span.
Austen basically said it all. I don't prefer a mulching mower for myself because they aren't well suited for real heavy mowing. But for someone with a small yard that doesn't what to bother with a bagger it's definately a good way to go.