The following lines from http://www.softwarefreedom.org/resources/2008/compliance-guide.html
seem to cover the case of someone who casually redistributes, for free, Ubuntu or whatever. Such can refer people back to the Ubuntu site. They should, perhaps, be familiar with the url, but I would expect that the binary Ubuntu distribution CDs have the appropriate offer and details on that disk. Someone who casually distributes, for free, a subset should also be covered. Under 4.1.2 Option (b): The Offer,
"The option to provide an offer for source rather than direct source distribution is a special benefit to companies equipped to handle a fulfillment process. GPLv2 § 3(c) and GPLv3 § 6(c) avoid burdening noncommercial, occasional redistributors with fulfillment request obligations by allowing them to pass along the offer for source as they received it.
Note that commercial redistributors cannot avail themselves of the option (c) exception, and so while your offer for source must be good to anyone who receives the offer (under v2) or the object code (under v3), it cannot extinguish the obligations of anyone who commercially redistributes your product. The license terms apply to anyone who distributes GPL’d software, "
Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
