All speeds of USB are compatible with each other, but the slower devices can slow down faster ones on the same USB connection (ie. same hub). Many digital cameras still seem to use 12Mb/s USB standard and not the faster 480Mb/s standard.
A couple of years ago the USB standards group decided to rename all USB connections to USB2.0 (apparently companies were having trouble marketing products with the older and slower versions). This means that now you need to look for USB "High speed" for the 480Mb/s version and "Full speed" for the 12Mb/s variant.
For some light reading here's a link:
http://www.usb.org/developers/packaging/
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