Well lets just say we have quite a few mac's in the office, and they come preinstalled with Photobooth... and when I'm asked to transfer a pretty young thing's account to a new computer, and make sure all her documents, emails and PICTURES are there... Well... they were.
And obviously there's always random questionable content in Downloads folders.
People not realising that every photo that gets taken on their phone gets sync'd to their iPhoto if they've got iCloud turned on, so they do something which opens iPhoto and boom... wife pics from the phone and much awkward silence...