We did 5 in one year - if we can count a B2B as two cruises!
We've done 4 in a year a few times, but average is 3. Very seldom do we do 2 and we only did one cruise once, which was our first cruise.
Guess you could say we're hooked!
Lately though, we've been doing less because we go for a longer period to do some sightseeing before and/or after the cruise. Like when we did our 12-night Baltic cruise, we spent 2-1/2 weeks touring around before & after, so we were actually gone for 32 days.
We just did a 17-night cruise from Hong Kong to Beijing that was awesome! Spent 8 days touring before and after that one.
But if we're not going to do any sightseeing, we've gotten so we don't like cruises that are any less than 10 nights. Much nicer to do the longer cruises.