When are Tweens Ready to be Home Alone?

It's a day that will eventually come for all kids, especially as they get closer to being a teenager- staying home alone- but when is an okay time for it to happen?
With summer around the corner and many parents facing tighter budgets for daycare or babysitters, children being at home alone is a timely topic as well as one that is debated in terms of developmental appropriateness.  NPR's Morning Edition addressed this topic last week with a story titled Home Alone:  Is Your Tween Ready?  While there is no cut and dry answer for all children, there are many factors to take in to consideration, such as maturity level, trustworthiness and the safety of your home.
Do you have a story about when you left your "tween" at home alone for the first time or any advice for parents getting ready to do the same?  Share your experience with us!