Can you tell me if there is a larger chance of Hard Drive failure rates for HD’s over 250GB?
There is a slightly larger chance at this time, but over the long haul, I'd rely more on my 1.5tb drives than my 250gb drives.
In any case, backups are essential for critical information, photos and the like.
The thing is you don't need anything bigger than a 250gb drive unless you're handling video files. And even then, adding hard drive space is a simple and inexpensive expansion - external 1tb drives are around $100 right now, internals are about $90.
I personally prefer the newer generation drives, as they're far quieter and remain cooler in the case, and are slightly faster.