The other morning I picked up Jerome Jerome the Metronome and said, "I can't believe people come in this size. What if everyone was as tiny as you?"
Here are my thoughts on that question: in some things, we wouldn't notice. Houses would be the same relative size, as would cars and chairs and tables.
What would be different would be the state of technological advancement. For instance, cell phones would just now be invented. Why? Because 80s cell phones would have been too enormous to be practical. Not until circuitry advancement allowed for modern-sized phones would we carry them around, and they would be as clunky to us as 80s phones were to the cavemen who used them.
Also, the list of "world's most dangerous animals" would be totally different. Hippos would probably not be the deadliest animal in Africa as they are now, because they would be the size of a house and only a fool would go anywhere near them. The number of dog-related deaths would be much higher than it currently is. Would dogs have even been domesticated? According to Jared Diamond's ideas, their living in a pack is a plus, but they are carnivores, which is a big minus, so probably not. (Right now Cristin is staring wistfully into the middle distance, saying softly, "For all sad words of tongue or pen....") Instead of being man's best friend, they would probably be our greatest nemesis. Saul Bellow's Henderson the Rain King would be about a man on a dog hunt.
What else would be different if a full-sized adult could expect to be 3'1"?