It is big.
That was my concern about buying the phone. My old phone fit very nicely in my front jeans pocket. The s4 does not. It fits in my back pocket, but sticks out the top and I feel like it's going to slide out whenever I sit down. I don't feel nearly as secure with the GS4 in my back pocket as I felt with a RAZR MAXX in my front pocket, so I had to find a new way to carry the phone. Ahh, progress.
That said, it is not too big for my hand, and I love the damn thing.
NOTE: This is not very easy to test in store. A lot of the stores that have models out for you to play with have them bolted to the display. Not to mention, the store security guy starts staring at you when you try to put their products in your pockets.