My G2 has been experiencing SD card issues for a month or two now. I've been exclusively on CM7 nightlies, but since nobody else seems to have had this issue, I assumed it was me. Usually when using something that accessed my SD card, the phone would "unexpectedly" remove itself. Sometimes a reboot would mount my card again (can't mount through settings), but oftentimes I'd have to wait it out and reboot after a few days/reboot 20 times in hopes that it'd read it. I would re-set my SD card in the slot several times, but it doesn't do anything.
I'm still at the mercy of it and am contemplating unrooting my device to bring it in for warranty because it is a very big issue that is crippling my phone. I purchased a new SD card, but the problems still persist. Multiple data wipes/rom changes have occured as well as formatting said cards, but it's all the same.
Right now I just flashed CM7 stable (card was working [it plays funny, but if I try to use the camera, it usually dies]), and I hope that my card issues are gone, but I am fairly confident it's a hardware issue.