What's the maximum length of USB cable that you can use for tethering?
USB 1.1/2.0 specifies a maximum cable length of 5 meters (~16 feet) as a function of a minimum required transmission speeds. That's pushing the limit, to some degree, and will be highly dependent on how well the cable is made, shielding, etc. If you're worried about reliability, I would go under that, probably no more than 3 meters (~10 feet).
USB 3.0 doesn't actually specify a maximum length, but we're still talking copper here generally, and so the maximum practical length is probably around 3 meters to meet the speed requirements, so on USB 3.0, I'd go less than that again, maybe 2 meters (~6.5 feet).
My source for this is Wikipedia which is usually pretty good at explaining standards items. In this regards, I'd probably trust them. In any case, 10 feet is a pretty decent cable length, but if you need much longer, you can also get USB repeaters, bearing in mind that you often get what you pay for with these.
So, in general, I think the limiter is most likely associated with cable quality as opposed to the camera. If the camera is truly specified to the USB 2.0 standard, going with a good cable smaller than the maximum, should be more than fine and use of a good repeater can help in extending that length as you need.
The hubs that are referred to in the above post are USB to ethernet converters. CAT5 Ethernet has a 100m maximum length.
@Mike, you're looking at the other answer on that question, not the one hyperslug linked to. And *ehternet* over cat 5 has a 100m limit, but usb over cat 5 has a much shorter limit, generally around 66m.
You're correct that the specified length (up to USB 2.0) is 5 metres, but that isn't a maximum theoretical limit, that's a minimum baseline - USB 2.0 is **required** to work perfectly with up to 5m of cable, including joins or extensions, as long as all that cable is certified (has the USB logo on the plug). To extend it further you need a hub or repeater at that point. Like many similar standards, you can probably push it much further and it'll work fine, like 10m or even a bit more, but the standard only requires it to work for up to 5 metres.
@thomasrutter: http://www.usb.org/developers/usbfaq/#cab1 in which they apparently disagree with you. In fact, on making a cable longer than 5 meters they respond with "Even if you violated the spec..." and doesn't change the fact that cable quality has an impact, a 5m cable may just make the spec and get the stamp, but still not perform as required under the right conditions which may be easily hit outside of a testing lab.