I have a Canon Rebel T3 and a Lexar Platinum II 8 GB SDHC class 6 card. I can only fit about 180 photos on this card that are roughly 5 MB each. Unless my math is really bad, that's only about 900MB ...
My wife has a Canon IXUS 960 IS, and she's finding that she is filling the 2Gb cards I'd originally got for her too quickly. I know that some cameras have a maximum supported capacity for memory ...