As Apple enjoys continuing growth and expansion into an ever-wider customer base, it also risks tarnishing its reputation for stellar service. On the sales front, everything is rosy. Macintosh computers are selling three times as quickly as the overall PC market, the iPod is burying its competition, and the iPhone is transforming the wireless industry. But with millions more customers, keeping them all happy becomes more difficult. This is a new world for Apple, which for years relied on a devoted core of tech-savvy fans clustered in the education and design fields. While Apple still ranks atop the customer service chart, its position is slipping just a bit. A University of Michigan study showed Apple going from 83 percent customer satisfaction to 79, its first drop since 2001. Complaints about Apple's policies and service have grown more heated on Apple-related blogs and websites. Yet by its internal measures, Apple states that its service has never been better. Its own customer satisfaction surveys show an increase, and it claims that 90 percent of tech-support inquiries are dealt with on the first call. Still, any crack in a pristine reputation can indicate more serious problems, and Apple may be more vulnerable exactly because high-quality service has always been a key selling point. For example, its Apple stores promise friendly, convenient service, but that matters little to people who live far away from one. Problems have also arisen because Apple's laptops, which are more subject to wear and tear, far outsell its desktops; also, the more gadgets a device like the iPhone handles, the more there is that can go awry.