I don't do it very frequently, but I used to work an office job where I usually started work half an hour to an hour before most other people even arrived. I also had a pretty flexible schedule in terms of my daily work, so slacking in the morning could easily be caught up by taking less breaks later. I might occasionally smoke up a little in the morning, and when I'd get to work with my high already wearing off, I could browse some shit on the internet, listen to some music and sip at my morning coffee as I settled into work in a nice, comfy way. Then I'd start working harder as the weed wore off and the caffeine took over. I wouldn't like to smoke large amounts, or smoke during the workday though, 'cause whenever I did that, time just passed infinitely slower. Plus, work isn't exactly fun, even when you're high (for most of us unlucky people), so it's a waste of good smoke. Gets your tolerance up as well. I'd rather wait until work is done and toke then.
As for school, there are some lecturers who are fairly interesting to listen to while a little bit stoned, but others are just impossible to follow. Being a little bit high, I find, opens up my mind to thinking in different ways, particularly understanding concepts as a whole and making connections. Smoking a lot is always counter-productive, though, and either makes my mind wander or makes me want to think about how painfully slow the lecture is progressing.