SDHC stands for SD high capacity memory cards, up to 16GB once they release that model next June:
http://gizmodo.com/341463/sandisks-n...gb-this-summer
(Panasonic is working on a 32GB model I've heard too :O )
Dunno, but 2-4GB is room enough for me :/
Anyways, I still think that the R4 plus a EZ 3in1 cart is the best solution if you want to have it all, high compatibily for NDS games, GBA support, rumble and the browser.