This recipe is boring. Use lemon juice, not lime. Lime adds a bitter quality that you don't want. I also add some finely chopped onion, diced tomato with the juice squeezed out, garlic, and a little sour cream or mayonaise (Yes really. I got that idea from a friend and it's surprizingly good.)
Some of the best restaurant guacamole I've had is at El Fenix. All they do is add fresh pico de gallo to mashed avacado with a bit of lemon juice. It's really good.