I've got a similar issue, with a jmicron based esata card.
after lots, and lots of experimenting, I've determined it must be a firmware/bios issue with the nvidia chipset and new macbooks. The card won't even work on vista at all, with a code 12 error, but will work in XP, but hot plugging does not work at all, no recognition, and if you safely remove the device it will not be recognised as removed, or reinserted. It works perfectly fine under OS X, so the hardware is clearly capable of it.
It also works perfectly well on a non unibody Macbook Pro. Looks to me like apple need to get an EFI update out there.