New York Times health columnist Gretchen Reynolds has had several articles lately (in the Science section) about the value of short-term intense workouts.
I’m doing this on a Versa Climber, but you can achieve the same thing by going fast up stairs, using a stationary bike or via other modalities.
You can get your heart rate up and blood circulating in a minute.
Also check out the new version of Stretching by Bob Anderson, which has stretches and tips for smartphone users to combat bad posture. Hold that phone up in front of you instead of bending down to look at it! Duh!