RAID-5 is a fault-tolerance solution, not a data-integrity solution.
Remember that RAID stands for Redundant Array of Inexpensive Disks. Disks are the atomic unit of redundancy — RAID doesn’t really care about data. You buy solutions that employ filesystems like WAFL or ZFS to address data redundancy and integrity.
The RAID controller (hardware or software) does not verify the parity of blocks at read time. This is a major risk of running RAID-5 — if you encounter a partial media failure on a drive (a situation where a bad block isn’t marked “bad”), you are now in a situation where your data have been silently corrupted.
Sun’s RAID-Z/ZFS actually provides end-to-end data integrity, and I suspect other filesystems and RAID systems will provide this feature in the future as the number of cores available on CPUs continues to increase.
If you’re using RAID-5, you’re being cheap, in my opinion. RAID 1 performs better, offers greater protection, and doesn’t impact production when a drive fails — for a marginal cost difference.