No doubt you could fit a lot of people shoulder to shoulder on this planet.Bottom line is there is a point in which we are going to 'overgraze'.A lot of land is not suitable for living,like mountains,deserts,and arctic regions.It also takes a considerable amount of farm land to keep these people fed.Takes a lot of fresh water,and concrete and the ability to control waste.This planet also needs forest and wildlife to keep things in check.I would rather not live to close to the fine line,once its breeched you get third world conditions.I think we are in store for a change in lifestyles in the future.The rate we can populate earth is also very dependant on the medical/science feild.When we pass them up or they fissle out we got probs.I dont have a answer of how many can live here,but its a little more complicated than just standing them up in texas,I think.Chances of the human race ever being wiped out is VERY slim,but the chance that more and more people live like etheopians in the near future isnt so slim,add a climate change(irratic weather) and it only speeds things up.