10 minutes walk, 20 minutes on the tube, 5 minutes walk - it's not too bad, leave home at 7-15 or so and be in the office for 8. Fit in an episode of whatever I'm watching that week in each day on my ipod touch (half in the morning, half in the evening).
Can't say I love it as it's busy even that early in the morning (and it's the northern line, so it will break) but it could be worse. Most I'd do is 90 minute or so (and I may do if I decide to move out of London) but it would have to be in one go, 90 minutes writing notes and catching up on the train is fine, but if it was constantly changing trains and getting on the tube I wouldn't do it.