My mom is one of those serial sneezers of whom you speak, ot. Without fail, she sneezes three times in rapid succession, then there's a pause of thirty seconds or so, and she has one final nostril-blaster.

I'm not typically a serial sneezer, but now that I've developed Midwest allergies, I've been known to get several in one sitting. My normal pattern is one if it's just a standard sneeze, two if I'm getting sick.