The striking realization for me with regards to PayPal usage (and how both reasonable it is to provide the option, as well as how many people must actually prefer to use it) was the day I noticed that Apple, a company that often is described as having the valuable asset "millions of customer's credit card details on file, ready for one-click purchase of anything on their Mac or iPhone", actually supports PayPal as a payment option in their iTunes suite.
Note that for an international business, PayPal has the invaluable benefit of supporting a huge bunch of national payment methods - in many countries, these are more widespread than credit cards, so if you want to do business with normal people there (like Apple), you have to support these methods.
