I feel old, in that my first DOS was 4.0, and remember the experience of "upgrading" (don't be deceived, it was a clean install) to 5.0, and then to 6.0.
I also remember being on campus for the Windows ME fiasco. I was an employee of the uni I was at, and was eligible for Windows 2000 Pro for the cost of the media. A whole OS for I think it was $14. Of course I'm upgrading from 98. And since I had just upgraded, I didn't immediately pull the trigger on the ME upgrade a few months later...and then spent the next couple years laughing at the people who did. (Not gonna lie, 2000 was one of the best OSes they cranked out.)