I have now "officially" started what I call Ten Mile Tuesdays in to my weekly running routine. While it's not a hard requirement to always be done on Tuesdays, the idea is that at least one run Monday through Friday be 10 miles.
Why? Because I have a race coming up soon and I don't want to be behind in training. A few more miles every week will help burn off the extra holiday food I'm certainly going to consume.
My average daily run is about 7.4 miles, and running 10 only takes an extra 20 minutes of running. Easy!