Unfortunately, my understanding is that the readers in all the late 2009 iMacs will NOT handle SDHC cards (much less SDXC). The newer generation of iMacs from 2010, will handle at least SDHC. It is my understanding that they will not handle SDXC - and worse, it is my understanding that Apple is not ready to get data off from SDXC external readers either! The way I know this, is because I bought a Panasonic DMC-LX5 camera, and also a guide to the camera wherein the author states that Apple does not have a native solution for SDXC cards... the only way he was able to get data from a SDXC card onto a mac, was through the manufacturer of the reader writing their own drivers for mac, and then going through an ExpressCard! In other words, there are very few macs which even have ExpressCards and then you have to get a special reader from a manufacturer who writes their own mac drivers. Of course, in time Apple will get around to fixing this issue (I hope!), and this info is a few months old, so maybe they've already solved it.