When I bought my house, the only thing left carpeted was the stairs, so I knew there were going to be issues with it. Well, here is what it looked like after I pulled the carpet a few years ago.
And here is how it looks today, as I spent the day scraping the old mastic from the carpet, and removing he screws the old owner had driven in, replacing five treads and such. Amazing how hard scraping is when you really can't put weight on stuff, and doing it on stairs is real tiring. Still a long way to go but looking much better.