My 4 year old hard drive is starting to fail. The SMART status is reporting difficulty reading some sectors.
Fortunately I caught it early using a tool called HDDScan, which reads the SMART status and does surface scans. The drive was under warranty (5 years on an older Seagate drive) so it was replaced. All the data was moved off before any information was lost. If it was lost I have an onside and an offsite backup, as well as online backups of some things.
Everyone should check their hard drives with a SMART tool occasionally!