I change mine with each new quilt. (I tend to work on one quilt at a time).

Carla

about every six hours or less if you're paper piecing or heavy quilting.

Teri

Okay, I have a really stupid question. Other than when I hear the popping noise, when should I change the needle on my sewing machine? I'm sure I must have known this at one time, but I've forgotten.
Eileen