For me it's an hour each way, but apart from the obvious health benefit it also serves as some sort of day markers. In the morning it's really good way to get you up to speed (increase heart rate, get some extra oxygen in), and in the evening it's perfect to finish and leave all the "work stuff" behind.
Added bonus - money saved on public transport, and no gym subscription required.
It's an uphill ride to work, so I bought a mountain bike with one of those electric assist motors to help with the sweat thing. It makes riding up a moderate hill no more taxing than riding a regular bike on flat ground.
I thought it would be kinda lame for regular bike purposes, but it actually works out well. The law here says the motor has to cut out at 25kph (16mph). And when that happens, because it is really heavy with the huge battery and motor, it becomes extremely taxing to coax any more speed out of it. But riding around at max speed feels still gets my breathing and pulse up.
So the upshot is that I still get a lot of moderate exercise from the bike, and I can locomote around Tokyo at a pretty much constant 25kph, using either the road or the sidewalk depending on traffic/pedestrian conditions.
And, because I can take a pretty direct route to work, I get there in half the time it takes on the subway.
We can also leave our details with someone here and they'll arrange for a bike service to be performed during the work day.
I've noticed a recent up-tick in companies (especially engineering firms - one of them sponsors the major cycling event in this country) embracing cycling as an activity and mode of transport. It's really good to see.