Spurs center Tim Duncan returned to his summer job at the Apple Store Genius Bar Monday, where he provided technical support during his eight-hour shift by diagnosing problems, troubleshooting software issues, and repairing people's computers, iPhones, and iPods. 'I can't stress to our customers enough that they really need to make multiple backups of their data,' said Duncan, who has worked at the San Pedro Avenue location for the past three summers. 'A lot of times we can retrieve files from a crashed hard drive, but you shouldn't rely on that. Also, you can increase the battery life of your laptop if you shut it down when you're transporting it from one place to another.' Duncan has also offered to take a shift for fellow Apple Genius David Atwood on Saturday, saying it would be a shame for his coworker to miss Game 3 of the Nuggets-Mavericks Western Conference Semifinals. 