You're one of the lucky ones. As a professional photographer, the main reason my wife got this device for me Christmas was so I can connect it to my camera in the field and download images without the need for the PC. Their website clearly states that this is possible. I have the correct cables/adapters and the camera (Canon 40D) is a powered storage device.
However, it does not work as promised and I am furious! We searched high and low for a device that would do this and have enough storage and thought we hit the jackpot when we found the Archos 70i.
Now we feel swindled and cheated as the device does not do what Archos promised. I loved the device at first but now I'm seriously thinking about demanding a refund for false advertising.
Which USB host cable are you using? It needs to be a Type A Micro
to USB A like the Nokia CA-157 or the like. A type B Micro to USB A like those that are more commonly found will not work as the A70 port does not get put into Host mode which is what you need it to do. I just tested this with my Canon T2i and Canon XT and it works great for me with both. I even ran a slideshow from the T2i's storage on the A70. As soon as I connected the camera it said "External Camera Connected" and it showed up on the Archos file system as /extcamera. I also tried copying files between the camera and A70 and it was faster than when I tried it with a USB stick.
Here is the one Allen uses http://search.digikey.com/scripts/DkSea ... nt_id=5042
and the one I use http://www.pimfg.com/Product-Detail/000-USB-MC-11
both accomplish the same thing. Please note the one I use is a 90 deg angled one that puts the full size port facing the rear of the A70 and may not be what you like. I only got it because it was cheap. You can get similar cables to the one Allen uses on eBay for about $4 but they ship from China and may take some time to get to you. There are several sellers of the Nokia CA-157 cable that should work as well.