USB 1.0 length max is 3 meters and USB 2.0 is up to 15 meters; both without a repeater.
This is the official norm... and then comes the problem of compatibilty with that hardware.
I know firsthand that my ADSL modem worked fine on USB2 with a 2m cable, but wasn't seen at all with a 5m (15ft) cable ; I discovered it was a known peculiarity of it and switched to RJ45 connection, which is a treat for long cable lengths (up to 50m at least IIRC).