How are these calculated? I see them going up and down all the time, and there are obviously way more than 48 questions about C# so how are these calculated?
It's basically looking at recently:
And then tossing out any tags that don't occur at least a minimum number of times in the whole database. A tag has to have some traction (ie. be a real tag people really use) to get into that list.
The exact numbers vary a bit site to site, but that's the gist of the algorithm.
This isn't really an answer, but I went to the newest tab, and counted how far the questions go, and here are the results (sorted by number of questions):