I crack my knuckles religiously, been doing it for years. My fingers start to get a little stiff if I don't do it at least once every 2 hours.

Don't forget to crack them at the 2nd joint down from the knuckle also. I also crack my toes, and I can crack my ankles as many times in a row as I want. They also crack sometimes when I walk up stairs. It's annoying sometimes.