I am doing 400 push ups every other day. I do 40 at a time, but I do them over an 8-10 hour period. Am I really benefitting from this?
Define benefit. If you want to do a lot of pushups, then obviously, you're doing the right thing.
But if you're trying to build an overall strong body, and pushups are the only thing you do, then no. In fact, if you don't compensate by at least working your upper back, then you will absolutely not benefit. You'll be contributing to muscular imbalances, and shoulders being pulled forward giving you a hollow chest.
You should get a proper workout program. Pushups should be part of it. Not all of it.
Doing a lot of push ups with proper technique may (but not with certain) help with initial muscular imbalance as you are pushing up your body weight. Overall though, I would not count on doing push ups making you ripped! :) You will reach a point, if you haven't already, where the benefit is not really applicable anymore, called a plateau, and basically you're just getting really good at doing push ups, not building muscle.
I've read that if you are not strong enough to bench press a barbell, doing body weight push ups can help increase your base strength as a means to get you strong enough for using a barbell for bench press. That being said you can also use lower weight dumbbells to assist in increasing your strength as well!
If you're goal is to build muscle and strength though, then at a minimum you will want to hit the weights and progress in weight. Progression is a key part, but not the only, in breaking down muscles to repair even stronger.
If you are interested in learning further, I get pretty much all of my information from http://www.muscleandstrength.com/
You are maintaining yourself in sufficient shape to do 400 pushups over the course of a day, and doing 40 at a time really isn't shabby either, Doing them in several phases over the day also means that you're training your body to be ready at all times, and to be functioning under different conditions including how recently you've eaten and what activity you've been up to lately. The one big catch you'll be facing is that, if it's become routine, you may not be getting any better. If those last few pushups aren't something you have to work at, if you just pump them out with nary a sweat, short breath, or tired arms, you're maintaining yourself at that level. Which, as I said before, isn't shabby, but it's also not continuously improving yourself.