The first thing I'd suggest is check your cable. I had this problem myself as the cable I was using was actually from one of my older cameras and it was only a USB 1.0 cable. Also make sure your USB ports are actually turned on in your system BIOS as well (never hurts to double check).
If that's not it, my next suggestion would be to download the latest drivers from Canon's website...completely uninstall the old ones first and then install the new ones afterwards (do NOT try and install the new ones over the old ones!). If it's still not working I would also look for TWAIN conflicts if you have something like a scanner or another digital camera's software install on that computer. May not be a bad idea to just reinstall the USB drivers too.
Beyond that, if all else fails, try installing the camera to a different computer...if it still don't work, it could be a problem with the camera itself (it happens).
Also on a personal note, I think card readers are a pain in the butt...I've had two of them crap out in a row so I just download right off the camera. Unless you have a really bad battery, the juice used to download your pics is relatively insignificant and as far as the wear and tear goes on the jack for the cable, I'd say this isn't any more or less of a problem than the wear and tear caused to the CF card slot on the camera by popping the memory card in and out all the time. To be frank, I see Canon cameras (and others) up on Ebay as damaged/for parts all the time where they've lost a pin in the CF card slot but I've never seen one listed like that because of a bad USB jack. Very simply between my Canon and my Sony, I've downloaded close to 30,000 pictures right off the cameras and I've never had a problem. Sorry but to me card readers are a waste of money.
Just my $.02 worth...hope it helps!
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