yes and no. they're a good exercise and the military uses them a lot along with pullups...but, you can really only gain so much muscle doing only those kinds of exercises. they are good to do though, i feel in addition to other exercises.
Depending on your arm placement (narrow or wide) they are primarily a chest and tricep exercise, They hit the upper outer portions of the pectorals, so if you did ONLY pushups, you would have an asymmetrical look. But they are a great part of a workout.
Yes, I agree. Pushups are great for the chest, shoulders and triceps. They are good for any workout and if you can't do them on the floor, you can do them against a wall.
However, you might want to add a bicep exercise and maybe one that targets the shoulders a little more.
Pushups done with great variation are great for the whole upper body. You ask about tone and I would say go for it. But if you mean definition then I would recommend other exercises. As meliris points out they are a bit restricted in the muscles they hit.
Try standing pushups - great exercise, can be done anywhere and if done right take in almost all of the major muscle groups! Usually these are touted as beginners, less difficult exercise but hey - I adapted them and love them for their all over body working.
Play around with your foot and hand placement. Remember to turn your fingers inwards as well as upwards. Keep your abs tight, your heels down and your body in a 'plank' position throughtout and you'll definitely feel the work.
I love pushups but they don't really work the biceps or back so you wouldn't get lovely arms and back from pushups alone. Like everyone else said you would need to supplement them with other exercises. I use them when I am working out my chest and I use triangle pushups on a tricep day.
One of the reasons I do bench press is to improve my ability to do pushups in Tae Kwon Do. I just earned my brown belt and the instructors require more and more pushups as we progress. But it took me this long to figure out I should probably also add more pushups to improve my pushups!
Carrie
Being ex-military myself - the best way to do more pushups is practise. Everyday do a set of pushups and gradually add extra ones. It is one thing that can be improved with repetition if you are just going for quantity. At my best I could do about 65 full body push ups with good form.
JC -- the trainers in my gym just had a pushup contest (for $$$) and the winner was able to do 63. You would have been able to beat all the guys! Too cool!