I've lost count of posts like yours and the makers are not limited to Ford, GM, Samsung, and all the rest that if you don't report the problem inside the warranty you often can't get a free repair.
But I missed where you tried to restore the machine to factory issued OS. If that fails I use some cheap USB sound card. Example at http://www.geeks.com/details.asp?invtid=ZM-RSSC-PB-R&cat=SND and a few are cheaper than that!
You make a fine case for extending warranties.
Bob
Just some information on the ACER Aspire 8930 laptop. I've had mine for a little over a year and converted it from Vista to Windows 7 a short time ago. Before that I noticed that the sound (audible) would work sometimes and others it would not. I thought I had caused the problem but after taking it into a specialized repair shop and having them try to clear the problem for at least a week they couldn't fix the problem either. After they called up ACER customer service/tech support they were told that these were well known to have this problem and since I was not within warranty (warrantly ran out 2 weeks earlier) I could not send the laptop in to them to have it repaired. I would have to purchase a new motherboard which would run about $950.00 and have it installed which would add to the charge. I'd only paid $1075.00 for the laptop so I decided not to pay for the repair. I understand that ACER is a very good company but the service in my situation was very, very unacceptable. I WILL NEVER PURCHASE ANOTHER ACER PRODUCT OF ANY KIND UNLESS THEY AGREE TO EXTEND MY WARRANTY AND REPAIR THE PRODUCT!! Thank you very much, Lon Stoll

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic