It may cost around half the price of the machine itself, but Apple now offers an official 8GB RAM upgrade, mysteriously only for 2.93GHz and 2.66GHz MacBook Pros. Wait, we thought the max was 4GB?
As we confirmed a while back, the new MacBook Pros technically support up to 8GB, but OS X starts to choke on anything above 6GB. This is almost certainly a software issue, as the hardware on the newer MBPs has not, to our knowledge, changed aside from the boosted processors.
So does that mean all of the Unibody MacBook Pros can now run 8GB of RAM cleanly? We're waiting on confirmation of that. The upgrade is only sold as an accessory, and is not available as a build-to-order option. And of course, if you shop elsewhere and avoid Apple's notoriously ridiculous RAM markup, you can probably get two 4GB sticks for significantly less.
For more info, here is a good thread on people's experiences running 6GB and 8GB of RAM on MBPs with an official 4GB "ceiling."