I've never gone out to do a specific stair workout, but I do climb a lot of stairs daily. I do this deliberately as part of my training and I can tell you that it works wonders. This is more specifically for my trail running and I can say with certainty how much stairs help for that.
At work I park on the 8th floor of the parking garage specifically to run down on my way into the office and then run up again to my car at the end of the day. I also walk the stairs everywhere else I go during the day and never get into a lift. This has the added bonus of not sucking up everyone's germs during the lift ride as well.
When I go to the bathroom or go to get coffee I walk up 4 flights of stairs every time instead of going on the floor where I work. Running down is also great practice. On average I climb 54 flights of stairs daily. That might not sound like much, but do it 5 times a week and I promise you will find yourself stronger on those hills. The 54 flights down definitely helps as well.
The best about this...it's all done as part of my daily routine and I don't have to make time for it!
The stairs are my friend, are they yours?