Do lots of people get intussusception, or is it unusual?

Rare. Intussusception is primarily seen in young infants. When seen in older children (over 3 years) or adults a lead point must be excluded. The lead point could be a tumor and the intussusception is the first sign.
Incidence is 4/1000. There are two classes of intussusception. First is children less than 2 years, where the incidence is fairly common and the cause is idiopathic. The second class is children great than 3 and adults, where there is usually a lead point which requires removal.
Common in children. It is most common in young children less than 5 yrs of age, however, it can occur in anyone.