How good is doing 10-20 push-ups every 30 minutes?
I worked with a group of people in my first job that started a push-up club, and we did something very similar to this - 10 pushups every hour, on the hour.
We all thought it was great. After just a week of it, I noticed that I looked more toned with my shirt off; I was fairly trim and fit in the first place, but doing 60+ pushups a day really polished what I already had going for me. I was also sore going into the 2nd and 3rd days of our new routine, but after I got over the initial soreness it was smooth sailing. My chest and arms started to feel stronger, too, which led to better sessions in the gym when I wasn't too fatigued.
After a few weeks our dedication tapered off, of course, and we quit doing it. But while we stuck to it I enjoyed the little hourly breaks from our work and the chance to occasionally get my heart rate up, which has been shown to improve everyone's productivity and overall morale in an office (or classroom) setting... None of which is probably relevant here, but hey, now you know even more than you asked!