I don't use a lock screen. When I press the "Home" button I want to get right to work. I turn my phone "on" hundreds of times a day and I don't need another step between me and productivity.
à la Mitch Hedberg, may he RIP:
You know that Pepperidge Farm bread, that stuff is fancy. That stuff is wrapped twice. You open it, and then still ain't open. That's why I don't buy it, I don't need another step between me and toast.
As for security, the phone is always in my hand, on my belt clip or my desk at home. I guess someone can break in to my house and steal it but I'll take that chance.
I see a lot of people using a single swipe to unlock the lock screen. I guess the only reason, that I can see, to use it would be so that the phone doesn't turn on in your pocket. But I think a lot of people don't realize that it can be disabled. Lock screens have become de rigueur