Push ups are a staple if you you do martial arts/boxing/kick boxing etc, so I used to do lots and lots of these, often several hundred per day.
Doubt they do anything to build size though or strength to be honest, as once you can do one push up you are strong enough to do push ups, anything after that does not get you any stronger, it just builds endurance and conditioning.
I used to teach and grade fighters and often some would complain to me saying that they are not strong enough to do the required 50 or 100 or 150 etc push ups required to qualify for a certain grading/level. I used to explain to them that once they are strong enough to do one, the rest is just endurance.
I used to be able to do 200-250 push ups in one hit, at this time I benched may be around 70kg, now I bench 130kg, so I am way stronger and bigger yet I can only do about 50-70 full push ups in one hit.
I think push up are a great conditioning tool for athletes and everyone should be able to rep out 50-100 push ups at any time, but I doubt they are of much use to build size and strength unless you are half dead already. I also believe they are a great tool for children to train and condition their bodies, both my children 8 and 10 both do push ups as part of their routines, my 8 year old son can easily do 15-20 full correct form push ups.