3.4 miles, work in office IT for a telco, so have a laptop in a rucksack. I wouldn't want to do more than 5 odd miles on the 125 but if I had a bigger bike, I think I would commute on it however far it was, as long as it was a realistic drivable distance.
We have a great scheme at work where if you don't have a car parking space, you get an extra 85 a month, so I bought a brand new ybr 125 on 0% finance, almost exactly the same monthly payments as the extra pay and ditched the car (you still get the "green" bonus If your on a motorbike) It's great, it's almost like work are buying my bike for me