5 gigs does seem like a lot to me as well, unless you buy tons of memory. I've been building computers (infrequently - 1 a year for myself and usually 1 more for friends or family) for a decade now, and while I'm clearly lucky I've never purchased a single faulty memory stick (I've bought corsair a number of times, usually their bargain stuff), nor had a stick fail on me. Come to think of it, I've been pretty lucky - I have tons of hard drives, internal and external, and one one drive ever failed on me (and not catastrophically, or even close), never burnt out a cpu or gpu while overclocking, or even had a fan fail on me.
Then again, maybe I'm not - at a previous job I was in charge of literally hundreds (I believe around 300) computers, most of which were on 24/7 and many of which were many years old. I only found a few faulty memory chips there. And for the record, yes, I do run memory diagnostics, at least on my own systems.