Is possible to use the Mp3 shield form sparkfun as an SD card shield... or maybe use the both shields in differnts arduino but with just one SD card. This could be a really good implement I think
PS: This could be in storage to... so if i put it in the wrong place move it pleace! 
PS2: sorry for the bad english!
Positive 07
I haven't used either, but I'd recommend you also take a look at the rMP3 shield from Rogue Robotics. Seems to be a more capable product... of course the price is higher as well. Not sure what your end use will be, but thought you might want to know it's out there.
Wooow this helped me a lot! thanks man!
adafruit also makes a nice SD shield - I based my Bobuino SD interface design after that.