I'm in the use sunscreen only if you have to. If you know you'll be exposed for a long period of time in the middle of summer then I use sunscreen. However, being more conscious about amount of time exposed, time of day, strength of the sun, recent tolerance (are you already tanned?) you can pretty much go without sunscreen.

To the people who won't use sunscreen at all, I challenge you to go out to a mid summer, midday Australian beach for 4 hours and no sunscreen. Let me know how it works out for you.