Hm, I/ve actually had it work very well. The code that I posted in one of my first posts logs all the desired data to the SD card that I have.
I'm using the sparkfun SD shield found here: SparkFun microSD Shield - DEV-12761 - SparkFun Electronics
The Arduino Mega has SPI broken out to seperate pins, so you'll need to run wires from that to the SD shield, but overall it works pretty well. Besides that fix, the rest of the hardware was pretty much plug in and go.