The new version of SdFat now supports the Leonardo for both Hardware SPI and Software SPI. It is sdfatlib20120719.zip at Google Code Archive - Long-term storage for Google Code Project Hosting..
By default Software SPI supports the pin configuration for 328 shields with:
/** Software SPI Master Out Slave In pin */
uint8_t const SOFT_SPI_MOSI_PIN = 11;
/** Software SPI Master In Slave Out pin */
uint8_t const SOFT_SPI_MISO_PIN = 12;
/** Software SPI Clock pin */
uint8_t const SOFT_SPI_SCK_PIN = 13;
To use Software SPI on Leonardo and Hardware SPI with other CPUs, edit SdFatConfig.h at about line 121 like this:
#define LEONARDO_SOFT_SPI 1