Pushups are a great exercise, and can not hurt- if you include them properly, and do them in moderation.
From your post i take it that you want to do pushups after EVERY one of your workouts. This, is a bad idea. Many people believe that your muscles grow while you lift, thus lifting the same muscle group over and over will bluk you up faster. WRONG, when you lift you create microscopic tears in your muscle fibers (this is why you are sore right after a good workout). If you do not give your muscles enough rest, and nutrients (protein, carbs, vitimans, minerals, etc..) they will NOT grow.
What i suggest for you would be to include the extra set, or sets of pushups to your workout once or twice a week. Like a 'finisher' to your workout.
Lets say your workout program calls for (chest/tri's) on monday. You can include pushups after this workout because pushups work the chest and triceps.
You could also include pushups again (if you feel you have had enough rest and your muscles are not sore) on 'back/biceps' day, lets say this is Thursday. Pushups also utalize the "lat" muscles in your back. It would be ok to do pushups again on this day because you have had a number of days to rest and recover. The most important thing is not to overtrain.
Hope this helps
-FD
