When did I do that task?

It can be very useful to see when I last did a repeating task, for example, when did I last see the dentist? If it's a routine task like this, then the interval between occurrences of the task may vary. On the Mac or PC, all I have to do is look in my list of accomplishments. On the iPhone or iPod Touch, it's not so obvious. If anyone has any guidance on this, I'd appreciate it.