Do lots of people get respiratory failure, or is it unusual?

Not unusual... There are lots of reasons for respiratory failure and some of them are rather common so respiratory failure itself is not all that uncommon, unfortunately!
Very common. Respiratory failure is very common, most patients in intensive care units require mechanical ventilation to breath and therefore have respiratory failure. In terms of chronic respiratory failure, where the lung function is severely impaired, one way to look at it is the chronic obstructive pulmonary disease ( copd, that is emphysema and chronic bronchitis is the nations 4th leading cause of death.