Arghh.... why the butt-raping?
Why 5400rpm drives on the 21-inch model? Heat dissipation when compared to the 27" one shouldn't be that much worse to not be able to compensate for the extra ~10°F that a faster drive will generate. That's just sh__ty on their part, since it seems that they're only purposely crippling the performance of the cheaper model, only to get you to buy the more expensive one.
Same with the price of the RAM: $600 is just usurious. Apple computers are a bit pickier when it comes to RAM (i.e., you can't usually expect cheapie, generic modules to work reliably), but their OEM memory is nothing special. Good-quality, system-specific RAM from Kingston, OCZ, etc
will work reliably and for a fraction of the price.
And as far as the drive upgrades, one could only expect these systems to have the same issue as the previous two generations when it comes to the HDD temp sensor, but I'm willing to put up with the noise (and/or a software solution to control fan speed) if it means not having to live with a slow 5400rpm drive, or not having to pay $250+ for a Fusion Drive configuration (which
can be replicated without a ton of effort, it seems). Specially true on the 21" model, which one can "only" upgrade to a 1TB Fusion drive. If the computer can fit a 1TB 3.5" HDD, it should be able to fit any 3.5" HDD (SATA interface limitations don't come into play until a magnitude of storage sizes later). Same concept applies to the second port for the SSD: while there might not be a bracket to hold a drive in place unless you order a Fusion Drive option, the port
should at least be there and be usable. Will have to wait and see.
For the time being, I don't think I'll be ordering any customizations, other than maybe a CPU bump.