I have an Adafruit data logger shield stacked on a Circuits@Home USB Host shield stacked on an Arduino Duemilenove. Recognizing that both shields defaulted to pin 10 for chip select, I modified the USB Host shield to use an alternate pin (pin 7) as described in their literature. Each shield works perfectly single-stacked with the Arduino. When double stacked, the USB Host shield works perfectly. When double stacked, the real time clock (RTC) function of the data logger also works perfectly. However, attempts to obtain card info or read/write to the SD card using the data logger example sketches fails to pass initialization. Both shields share SPI data lines. Is there something unusual about the data logging shield that will not permit sharing the SPI bus? I'm stuck.