I was trying to transfer images from my camera to my PC over the USB cable; when I connected the camera to the PC, it was automatically assigned drive letter H:.
During the transfer, Windows XP bluescreened. Yay. (not)
I rebooted and tried again. This time, the camera was assigned drive letter L:. What?
*opens Explorer* Yup. The card reader is recognised again, which explains the different drive letter. No idea what happened.
But yay. Now I could transfer images directly from the SD card rather than having to go card->camera->USB cable->PC; this went quite a bit quicker.
Let's hope it stays this way.