I have a microSD card shield from Sparkfun (http://www.sparkfun....roducts_id=9802) and a Sandisk 8GB microSD card and the code shown by Bob doesn't appear to work.
No, it doesn't support SDHC, so nothing over 2gb.
MicroSD is tricky, I've been reading the specs lately. All the other SD standards mandate SPI support, but Micro does not, so it might be hit or miss with getting micro cards working. Probably going to vary by make/model.