In order to prevent this I bevel my week. M, T, Th I set my alarm for an hour earlier. W and F I set my alarm for the latest I can reasonably wake up and still make it to work on time if there is a minor hiccup. It prevents me from getting used to a particular schedule and waking up ahead of my alarm. When I wake up ahead of my alarm I tend to turn it off, thinking I'm awake, and subsequently fall back asleep, making myself late.

Sleeping in on Wednesdays gives me a burst of energy just as everyone else is experiencing the mid-week "hump." And doing the same on Friday keeps me from checking-out an hour before the week is done. It's a good system.