I used to buy new ones every few years. But I was happy with XP when Vista came out and later decided to wait for 7. When 7 came out I was still happy with XP and heard good things about 8. But after seeing 8, I didn't like it and am now considering 10. But still happy with XP!!
OK, but you could still have bought XP (or get it for free) and put it on a new laptop. Has this occurred to you??

Computer technology (and price) has been improving so fast, there is simply no reason not to buy a new one after 4 years. All our laptops working in the house because I can fix them, but every once in a while we buy a new one...