I just ran for 20 minutes continuously, and from this useful website, I can tell you that I ran 2.4 km and burnt 852 kJ (one advantage(?) of obesity is that you get to work harder when you exercise)... After the 1st 5 minutes (during which I wheeshed and puffed like a tank engine), I found a comfortable hippo-trot, and it didn't hurt again until I got stitch right at the end. I'm pretty pleased given that my aim is to be able to run 3 km in 20 minutes (after swimming 6 lengths of the real pool and cycling 10 km) by February. My workmate and I are planning to do the Palmy TriWoman triathlon before we turn 40. She's got a couple of years, but I totally have to do it this summer!
I swam 1 km yesterday, and we're swimming again tomorrow (and we walked at lunchtime today too... I am such a jock), so now I just need to overcome the cycle-vertigo I developed during pregnancy and get on my bike and ride :-)