Hello
You could fin useful help in this thread :
http://forums.digi.com/support/forum/viewthread_thread,5590_offset,0
I have not (really) tested yet, because my system is for industrial use, i need to be sure i could read/write in the SdCard in all “conditions”, and if i have issues with SdCard, be sure to have official support.
I wait for a RCM6700 to try on it !
I love MiniCore, but… Rabbit is not the easy way 
For the moment, i use an mega328P / WinAvr / Fat32 lib to add SdCard support to my system, MiniCore send information to the mega328p thru one of his rs232 line, crazy no ?
Yes… i add a small 16mhz chip to add SdCard support to my system !
I would like the RCM6700 become the new heart of my system, official SdCard support is mandatory to have a real allround “system”.
But, official SdCard support on RCM57xx or 67xx is an old demand, in this end of 2011 no official support, application note or sample in the latest Dynamic C to do that.
Actual features of RCM6700 with official SdCard support could be a very good answer of lot other “all in one” easy to use solution like Arduino, Fez Domino, mBed, and so on, for the non professional community too.
For non professional or professional users, i’m sure official support of SdCard on RCM57xx or 67xx would be amazing (yes ! Ethernet and Sdcard on MiniCore !!), but support say you could buy the RCM4300 Series, with SdCard support bla, bla, bla
Same thing for 1-wire support : you could buy Simple Sensor Application Kit (the only way to have the official 1-wire lib), bla, bla, bla.
It’s a pity.
Hope Rabbit Semi could ear this demand 
Good luck and welcome in the Rabbit world !