So, I'm using a stripbaord arduino running at 3.3v (no need for level shifting) with a 16x2 LCD screen and a Sparkfun Micro Sd Card module (Link Below). There also an IR receiver TSOP31238 to receivethe signal from the pit wall. The SD Module is hooked up to pins 10 through 13 with 10 being used for the CS pin. Reading and writing to the sd card isn't a problem it just its standby current.
http://proto-pic.co.uk/breakout-board-for-microsd-transflash/
I'm testing with 2 different SD cards one is sandisk 1gb and the other is sandisk 128mb (quite old), both give different results, the 1gb increases the running current from 13mA to around 25mA (this is will last 24 hours ok) the other runs at 40mA (this is not ok and I need a system that isn't dependant on which type of card I use).
I've seen the quote before about the sandisk automatically sleeping when the clk signal isn't received for 5ms or more but i'm not sure if the arduino ever stops the clk signal? and if this is relevant in SPI mode?
I've also found out that some current is always leaking through the clk and data pins once the SD.Begin() is activated so this maybe a problem with the SD libraries on the Arduino as you can't 'Stop' an SD Card. Because of this its seem its very difficult to add a MOSFET to switch either Vcc or Gnd off when the cards not required ( the sandisk datasheet also states that power must come on to Vcc before power is received on the clk or data signals as this could corrupt the card and without being able to 'stop' the sd card this would happen)