Do lots of people develop confusion, or is it unusual?

Lots. Confusion is common. Transient confusion can occur from intoxication, drug abuse, head injuries, or acute illness among others. Chronic confusion is more serious and needs proper diagnosis and treatment. Even transient confusion if not from a clearly identifiable cause needs evaluation as it may be a signal that something serious is going on.
Yes and Yes. Confusion is not a normal state of being. On the african savannah confused animals get eaten. Do a lot of people develop confusion? Yes. For a number of reasons ranging from dehydration, infection, medications, hormonal imbalances, electrolyte abnormalities and age. Age-related reasons aside, confusion may often be reversible once the underlying cause is identified.
It is unusual. Confusion is disturbance of consciousness with decrease ability to focus. It is also change in cognition. Confusion could be acute or chronic or acute on chronic and could be caused by many factors some of them are transient and reversible and some of them are severe and/ or irreversible. For instance dementia is a chronic irreversible form of confusion. Drugs can cause mild or severe confusion.
Unusual. Human's brain is very brilliantly built like a great pc. Confusion is indicator for malfunctioning of the brain. The cause of confusion is vast and varies upon different age group. Most common cause in the young population is drug, infection, illicit drugs. Whereas in the older groups, stroke and metabolic abnormalities such as undetected diabetes could cause confusion.