A board full of Apple apologists, as always.
Frankly, I'm no Apple apologist. After my recent experience they are about my least favourite computer company on the planet.
But the other posters are, imho, correct. I thought it was a bit crap that the 15" MBP didn't support 8GB RAM when plenty of cheaper PC laptops were beginning to BUT.... I *knew* it didn't support 8GB RAM.
It didn't promise to support 8GB RAM - it quite specifically said 4. There was no reason to expect it to support 8GB RAM. Similarly I know my current laptop supports 8GB but I also know it came with a 32bit OS (Vista) so that I would have to spend money on replacing that if I want to take advantage of the 8GB capacity, and I made an informed decision based on that. I will not now complain if Toshiba start selling solely 64 bit Windows versions with their laptops. At most I might decide "oh, should have waited" but that's unlikely - I needed the laptop and it was a good buy. And even if I do decide "should have waited" that's feedback for me and my future decision making - not a complaint against the manufacturer.
You bought your MBP knowing it supported 4GB. It was not unreasonable to expect 8GB support in the near future, but it was not reasonable, given that RAM limitations are usually hardware based (given the Macs already have 64bit OS), to expect that support to retroactively appear in an older machine. If you didn't realise that, I'm sorry, but it's NOT Apple's fault, as much as I currently loathe them.
Re the point someone made about the chipset supporting 8GB, yes, but presumably there was a reason Apple weren't saying "8GB" when their competitors were and if one bought it on the basis that some components could support 8GB you took a CHANCE knowing it was a chance, it didn't pay off - factor into next round of decisionmaking. Yes this may have been cheap on Apple's part. Yes I do think they're shafting their customers by cutting tiny corners, and this is a worryingly consistent trend afaict and one of the reasons I'm no longer convinced their products are worth the price. But they delivered what they promised in *this* case.
As for the SATA thing, yes, it's crap. I agree totally, because you didn't/couldn't know. This is therefore a totally different situation. If they update their specs page to clearly state 1.5Gbps SATA1 then the comparison will be valid. It would still be crap, but you would know. This is how I felt about the 4GB limit - it was crap, but you knew.
Also, yes Apple has been known to under-specify RAM limits in the past - another reason to dislike their way of operating - and I myself wondered at the time whether they might well actually support 8GB but had 8GB support been a requirement I would not have bought one, or I would have bought one and expected that I might need to sell/replace it soon. I sympathise with and can understand the OP's situation, but it is one they put themselves in. But again, it was a CHANCE. A decision made in the full knowledge that you didn't *have* full knowledge. You every right to be disappointed, but the disappointment is the result of your choice. If they'd advertised 8GB, or even if they'd advertised an 8GB-capable chipset then said nothing about the actual capacity of the machine, I would be with you all the way (it would be the same situation as the SATA appears to be).