Sleeping in a cave

Well alright, not really a cave, but pretty close. The last 4 nights my family and I have been sleeping in the basement. My wife and I have been sacking out on a futon in the theatre, and my boys have been sleeping Gilligans Island style in the hammocks that we got for them in Mexico in their playroom (which is really a 5'5" finished storage area in the basement.) We wanted to do this because we have been having unseasonable warm summer weather lately and we just can't make ourselves run the AC all night. In doing this little experiment we have found a couple of things that I wasn't expecting. Our basement stays just the right temperature all night with only a fan running on low. Our perfect temperature is something like the cool nights of fall or early spring when you can have a thin quilt on and not sweat, or be cold. We've also found that without the sun shining in our bedroom window, that we can sleep really really well. Too well infact, I was almost late for work today because I was sleeping so soundly.
I don't know if we'll keep this up all summer or not, but we will most likely do it until the weather cools a bit. It will be interesting to see how or if this will affect our electricity usage this month, but I has certainly been worth it.