Hard drive failures have historically followed what we call a "bathtub curve". In other words they typically have a high (greater than 5%) early life failure rate that tapers off quickly to a very low (less than 1%) failure rate that sustains for 4-5 years and then begins trending back up. Personally I've seen some hard drives fail within the first few weeks of use while others lasted far longer than expected, into range of 7-8 years.
Occasionally a drive manufacturer will produce a specific model (or sometimes just a particular manufacturing lot) that has a much higher than expected field failure rate. I have seen this from every vendor, it's not limited to a specific manufacturer. If you hear someone say "I"ll never buy another (Western Digital, Seagate, Toshiba, etc.) drive again!" it's usually because they had an experience with one of these models.
Overall hard drive failures tend to be pretty low. Buffalo doesn't manufacturer hard drives, so when you buy a USB drive from Buffalo the actual drive inside the enclosure will be manufactured by WD, Seagate, Toshiba, or some other HDD manufacturer. Don't drop it or subject it to extreme operating temps and it will likely outlast the warranty. That being said, never keep your data in only one location. Always have a backup! Hardware does fail.
