The last frost day in my neck of the woods is around Memorial Day; I do cheat and set many of my plants out around May 10th or so.
I have a microclimate here created by a large hill behind my garden; many times I've gone into town on an early morning and noticed frost whereas there wasn't any at my place.
The last frost day is a good rule of thumb to follow. Being impatient and planting outside too early can cost you dearly. Nothing worse than raising some nice lush seedlings, to lose them to an unexpected freeze