I've just plugged in my camera to my macbook, its a Fujifilm Finepix F20 camera, and whilst the camera says its in USB mode, my mac won't bring up the drive for it. Tried both USB ports.
First thing to check would be the System Profiler which you can bring up easily by bringing up 'About This Mac' from the Apple menu and clicking More Info. Then select USB from the Hardware section. Does the camera appear there? If not, try a PRAM reset (with the camera disconnected). Steps can be found @ http://support.apple.com/kb/HT1379. Have you tried connecting with another computer? It could be the USB cable. An alternative would be using a card reader to read the SD card and trying to read from that.