Well, let's say you have $50,000 to put down on a house. If you go ahead and sink that into a property, you've just lost $50,000 of liquid cash that you could've invested in stocks for a (potentially) much higher rate of return. Ownership of a house includes all manner of hidden costs in maintenance, repairs, and the ever-popular renovations. Let's say, and this will never happen again in our lifetimes, the value of your house skyrockets in five years and you put it on the market for $50,000 more than you bought it for. To see that $50,000, you first have to sell it and that can be alot harder than the TV shows like to make out.
However, you have to, of course, factor in all the soft costs like: needing a roof over your head, desireability to have dominion over your living quarters, needing a fenced yard for your dog, needing to avoid busy streets if you have children, etc. Ultimately, because of these soft costs, and the simple fact that owning is an investment whereas renting simply is not, owning > renting.
BTW, I'm renting right now after selling my house and very much look forward to buying something in the spring. Even if I put half of my savings down on it. It's worth it to me....and the market is on a slight downswing here. I don't expect to ever make as high of a return as I did this Fall.
But then I became 
