I'm going to start with my own experience with Apple tech support:
I first got my PowerBook in August. At the time it was running OS X.3.4. Since the first time I got it and throughout the entire time I ran Panther on it I never had any problems except when I ran the DVD player app. After using the DVD player I would get what looked like dead/stuck pixels all over the screen that would appear and reappear at random. If I put the computer to sleep they would disappear until the next time I used the DVD player.
Well, considering I don't use my computer for DVDs I never really cared about the problem because it never happened any other time. That all changed when I installed Tiger on my machine.
During the install everything worked fine, but once the computer got past the gray Apple screen and into loading the actual OS I started seeing the same thing I saw in Panther after using the DVD player. I was able to take a screen cap, which can be seen here
These artifacts were there the entire time the computer was on and running Tiger, yet if I installed Panther again they disappeared. I did a straight upgrade the first time I noticed it and then did an erase and install after to see if that helped anything...it didn't. Since computer is still under warranty until August, I decided to wait until the 10.4.1 update before I did anything about it. The system seemed to be running fine otherwise, and the artifacts weren't so prevalent as to be completely annoying.
10.4.1 came out and I still had them so I called Apple up and explained the situation. The guy I talked to first had me go into the firmware and reset the NVRAM and the firmware itself...didn't work. We tried a couple other things and he said it was possible that there was some corruption from the previous file system. I didn't think it was the case, but I did what he told me to just the same incase it did make a difference. That night I went home and zeroed the hard drive and reinstalled again...didn't help.
The next day I called up again and was transferred to a specialist who said it was most likely a video card problem. He offered to send me a box that I could use to ship the computer to them for repairs, but I opted to take it down to the Apple store so I could have someone actually see the problem.
That Saturday I went down to the Apple store and showed the problem to one of the Genii. He hooked the computer up to an external drive and booted from it, and when it booted the problem was gone. I freaked out because the last time I went to the Apple store with a problem—with an external enclosure and hard drive, not the computer itself—the guy did the same thing I had been doing for three days prior and it worked right away.
Fortunately I had the sense to ask the guy if the external drive had Panther installed on it instead of Tiger. It did have Panther, so I asked him if he had a DVD he could throw in to see if the problem would happen. He did have a DVD and after DVD Player started up there they were again all over the screen.
I left my computer at the Apple store and they sent it off to the repair centre. Every day last week I was checking the repair status page to see how things were going. At one point I noticed a hold on the repair but it disappeared quickly only to be replaced by another hold with a cryptic description. I asked in one of the Mac forums on LiveJournal about this particular hold and someone told me that when that happens they've usually found a problem that isn't covered under warranty and need to talk to you about it.
I didn't get any calls and the next day the hold disappeared and the status was that they shipped it.
I didn't get an email saying they shipped it so I kept checking the site to see if they'd put a tracking number up there for me, then the realisation hit me that maybe, just maybe, it got caught in my spam filter. Not only did I find an email saying they shipped it already, but I found one saying they needed me to call them because they found a problem that might not be covered under warranty...uh oh.
I called the number and when I got ahold of one of the support people he checked and found that, apparently, the first person they gave the computer to couldn't find the problem—which means he must've been blind—and that's what prompted the email. They gave it to their second level support people, however, and the problem was seen immediately and the logic board was replaced making the problem disappear.
Needless to say I was happy about that.
I asked the guy if I could get a tracking number for my computer and he went into the system and found that it had already been delivered at 11 in the morning. From this point I had a little problem with DHL because the delivery person said that I signed for the package but instead just left it on the porch where it sat for several hours until someone came home
Not Apple's fault, however.
When I got home I opened the computer up and inspected it...everything was the same, right down to the scratches on the battery. I was very happy to find out that they didn't remove my extra memory stick, and after turning the machine on for the first time I was ecstatic to find out that they didn't format the drive!
I was hoping they wouldn't have to format but I knew it was a possibility. That's why I made sure I made a backup of the drive before taking it to the Apple store JIC.
The computer came back to me, a week after being sent away, exactly the same as it had left, except now my pesky pixel problem was completely gone. All in all a very positive experience with Apple tech support.