VoodooSDHCI did nothing for me, so I did some minor changes to be able to build Brendon Allen's and Forest Godfrey's SD card reader driver under Mountain Lion in 64 bit mode. (Source: http://osxsdhci.sourceforge.net) The included kext is x86/x86_64, but I'm on 10.8, so I have no idea how well it works in 32bit mode (but in that case you're well off with the original driver). I built it against 10.7 framework, so Lion people can probably use it too. Sources included.
I happened to have the exact same card reader as specified in the original Info.plist, i.e. 197b:2381, so I figured "whatever" and went for it. It's been 6 hours and I'm basically done. If you have a different device, you can try to edit the Info.plist file and change IOPCIMatch. For example:
$ lspci -vvnn | grep SD 06:00.2 SD Host controller : JMicron Technology Corp. Standard SD Host Controller [197b:2381] (prog-if 01)
Then you should edit your Info.plist to look like this:
(Note the reverse ordering of the vendor and device IDs.)
For the moment I have disabled
Any feedback welcome. This is a debug binary, so prepare to have your dmesg spammed.