iPods have been criticized for alleged short life-span and fragile hard drives. A 2005 survey conducted on the MacInTouch website found that the iPod line had an average failure rate of 13.7% (although they note that comments from respondents indicate that "the true iPod failure rate may be lower than it appears"). It concluded that some models were more durable than others. In particular, failure rates for iPods employing hard drives was usually above 20% while those with flash memory had a failure rate below 10%. In late 2005, many users complained that the surface of the first generation iPod Nano can become scratched easily, rendering the screen unusable. A class action lawsuit was also filed. Apple initially considered the issue a minor defect, but later began shipping these iPods with protective sleeves.[citation needed]

What are two subjects of criticism of iPods?