I'd have to say that the BestBuy in our area isn't all that bad. Do I know more about everything in the store than any of the sales people? Yes. Are they extremely taken aback when I waltz in and know exactaly what I need? You bet. But they normally have stuff in stock, the sales people seem capible yet poorly trained. But then again ... where we are, there is a Circut City right across the street, Comp USA a block up, and EB Games and Gamestop within 2 miles. Maybe the ammount of other stores allows them to keep stuff in stock or maybe they're just more "on their toes" because of all of the compititon in the area. I think that's a bit bogus though, because honestly, look at all the salepapers .. everything is the same price, and even if it's not, they all say they honor competitors deals. I've had one warrenty through Best Buy on a 57 inch RCA TV. I had one problem with it, picture tube went out, guy was there a day later and fixed it.
I worked for Whirlpool's customer service center for a long time. Behind closed doors, their idea was "If it's under warrenty, we're gonna do the work, find the parts, and deal with the customer's needs on our own time. If they pay for the work, we make a lot of money, so we'll be more attentive" Don't think the rest of corporate America is any different. Their loyalty isn't to you, it's to the shareholders.
On the topic of pre-build vs. custom machines -
I've owned one custom machine, from Gateway, and it was awful. Maybe because Gateway is awful but I dont know, I've never had another one since. I've had my share of problems from pre-built machines but I'll say this, Emachines has always taken care of me. For those of us who do more than sit in front of our computers all day, a pre-built machine is just fine. The last emachines I bought lasted a good two years, not bad for 400 bucks. Then it did about the same thing the OP is talkin about. Heard a loud 'pop' and the area around where my power supply was plugged in was blackened, power supply failed, sent a surge through the motherboard and fried it. I called Emachines on it because as it clearly states on the BestBuy recipt it ain't their porblem after 30 days and I didn't get their extended warrenty since it was almost the price of the computer and they only offered a 2-year plan.
All I did to that machine was stick in 500MB of ram and a decent video card ... GForce 4 i think. And it ran FFXI wonderfully. Since it died, Trippy has pirated my video card and ram. So a week later Kyp and I went out and got me a new machine. Right now I'm running another Emachine, couldn't tell you my processor speed, nor my RAM. All I can tell you is that it ran FFXI right out of the box without even cracking the case. I lag a bit more than normal, but tests have proven that it's the ram. But still ... I run a new-gen MMO on a friggin chip set! How awesome, and only $378, and it has a full 2 year warrenty from Emachines, who offered to extend it to 5 years for about half the price since I had a reported problem with my old one.
In the end - extended warrenties FTW. Allows the store to take care of your problems or farm the work out to a local company they've allied their service department with. If it's a really expensive item (I'm talkin a full kitchen set) It will also give you a little pull with the customer service dept. (or at least it sure did at Whirlpool) And highest quality is not always the best option, just get what you need.