My July '07 MBP
I have no idea where you are located, but I went to the Apple Store in The Woodlands (Houston, TX) YESTERDAY (9/12/07) and bought the exact model you are talking about. I even talked to the representative there about the yellow screen problems and my concern that I might be one of the unlucky few. She went and asked around the store and not a single person there had even heard of the yellowing and things of that sort. They have never had one returned or repaired at that particular store with these problems. She was even going to let me turn mine on in the store to check it out before I left. (because I live about 75 miles away) I trusted her word that they have had no problems at that store and I took mine home untested.
When I got home and took it out of the box, everything was as I would expect. No misaligned keys or screen, no yellowing of the screen, no flickering, JUST PLAIN APPLE PERFECTION. I couldn't be happier.
You just have to keep in mind that you aren't going to find people raving about how problem free their new purchases are on message boards. You are always going to find the people that are angry and want somewhere to vent.
I for one had a great experience yesterday buying, and setting up my new MBP.
I recommend going ahead and getting the MBP now if you really want it. If you can go to an Apple Store, even better. Talk to your sales person about it, and if you are really concerned, have them open it and boot it up and check it out right there before you leave.