I normally stay out of discussions like this mainly because there are so many variables as to why or why not a company would upgrade an OS. In the end any company that is properly managed needs to look at the overall gain of any upgrade.
Now on the personal front, if you are going to continue to upgrade hardware and software you will eventually need to upgrade. As for maintenance I never had issues with XP. I did upgrade to 7 and have had no issues with it. 7 loads faster than XP without a doubt. I cam't really say it runs any faster, but it defienetely does not run slower. As for Win 8, well I just don;t see the need.
I remember IBM DOS, MS DOS 2, 3,4, and 5, which by the way was the precurser to Windows with it's shell system, DOS6, Win 3, 3.1, NT, NT SP4, 95, 98, ME (yuk!) 2K, Server, XP, and 7. I left Vista out because I had no need for it. But I know a few people that are running it today and they have had minor issues, but nothing that is earth shattering. What 8 does is take a step or two backwards and that is not consistant with the model that has made MS the only horse in a one harse race. Was that smart or stupid remains to be seen. What annoys me more than anything is what I read in the thread about MS trying to block apps that bring back the start button to 8. If they don't want it in the relaese fine, but don;t stop people who want it there from doing so. I don;t like companies dictating to me what I want or need. That is my choice not theirs.
Have a great day!