As a certified computer technician (one of the many hats I wear) for over 10 years, I can tell you i've seen many technicians snoop and view images on a customer's system (while running an antivirus scan, or anything else time consuming). If you think for one minute that your data remains confidential with a unsupervised computer technician, think again. In my years of experience as a technician, I've come across pornography and completely legal pictures and videos of young-looking adults that are labeled as "teens" that are watermarked with images from legitimate adult sites (think Girls Gone Wild type stuff). With this law, I can't make that distinction anymore on whether or not it's appropriate to report or not, because if I didn't, and it actually was, I would be criminally liable. In doing so I would be forced to literally ruin a person's life (and lose a customer) by merely REPORTING it. If you think getting the authorities involved is harmless, I know first-hand how these criminal investigations go when it involves discovering possibly "illegal" content. They typically start with a raid in cooperation with local law enforcement, taking all computers, flash drives, discs, hard drives, anything that has data on them (usually making a mess of your house while doing it), and shipping them off to a forensics lab. This usually takes months, and (depending on the jurisdiction) in some cases years, to complete and get your systems back (presuming you're innocent) and to clear you of any wrongdoing. This is of course presuming of course the police, or your neighbors, or the repair company hasn't gone to the media yet.
Learning to use TrueCrypt (www.truecrypt.org) is a great start to securely store your files and keeping them from prying eyes, and storing your private files on a flash drive that you keep with you when bringing in a computer for repair.
Furthermore, use removable "flash drives" to keep your sensitive documents secure. I'm not talking about pornography here, I mean bank records, confidential work information, medical documents, ANYTHING you don't want someone else seeing. And it's more than just pictures that technicians scour over -- anything you don't want someone else viewing should be securely protected, because in my experience, there are plenty of technicians out there that intentionally stick their noses where it doesn't belong, and depending on the work being done, unintentionally.
Think of the children? Ha! Tell that to the high school kid who has naked pictures of his 17-year-old girlfriend, and who's now charged as an adult and labeled as a pedophile and sex offender for the next 25 years.