Thanks for the response once again.
When you say discrete, does that mean the GPU's in the 15 and 17 are user upgradeable?
For the MBA, when do you guys reckon that they will get Sandy bridge?
I might buy the new MBP and throw in an SSD, take out the CD drive and put the HD that came with it here... would that void the apple care? 5400 rpm is a bummer
The GPU in the MacBooks are not upgradable. In fact, GPUs in laptops never tend to be upgradable. If I recall correctly, "discrete" means the GPU is separate from the CPU, and does not use other system resources, such as the system RAM, to make up for the GPU's RAM. Hopefully someone can confirm if I'm correct or not.
Tthe future of the MacBook Air is hard to tell. The MBAs were updated not too long ago. The MBAs might start to use the Sandy Bridge CPUs in the next update, whenever that is. It won't be any time soon though, as Apple probably had a hard enough time fitting the Sandy Bridge CPUs in the 13" MacBook Pros, never mind the Air.
Using Optibay will void the AppleCare Warranty. You can always upgrade the primary hard drive itself via Apple's Website, or even by yourself. In fact, it's generally suggested that you purchase the cheapest Hard Drive and RAM from Apple's website, and then upgrade them both via 3rd Party resources. In other words, go with 4GB RAM, and a 5400rpm/7200rpm Hard Drive, purchase a Solid State Drive, and upgrade the MacBook yourself. It's not difficult, and there are tutorials everywhere.
Again, while I am not too experienced in the field, I think one of the most common suggestions for the 13" MacBook Pro is to go with the low end CPU, and purchase a SATA III SSD, which will be coming out this year.
The hard/solid state drive you pick from Apple's website is your choice. 500GB is usually enough for most people, so I'd go with the 7200RPM HDD. $100 isn't a bad upgrade deal for a 128GB SSD from Apple, but they tend to not be as fast as the competitor's SSDs. If you have a Playstation 3, or another Mac, you might want to go with that for the heck of it.