Many times I hear about GPL violations in vendors software, especially it seems in embedded routers. There are two cases which hit me in my home.
The first is our FIOS router which is an Actionec MI424-WR which runs Linux inside. You can even get to a telnet prompt. The problem is that it has a crappy DHCP server and always seems to assign different IP addresses even to the same MAC address. This breaks ssh and other services which do strong man-in-the-middle prevention. It seem the vendor hasn't fixed the problem, but as a result of a GPL violations suit the some source is available but the DHCP code is not included probably because it is BSD licensed so they don't have to. Given this I'll just punt and do the lazy solution and just turn it into an dumb Ethernet bridge and use something better like Vyatta V514 test box or Linksys WR54TG, both of which are repairable.
The second is the Asus P6T motherboard which has a SplashVM feature. This allows booting to a lightweight desktop in less than a minute (the BIOS is still slow to get its hardware setup). The desktop is based on Linux with standard kernel and browser. It is kind of a toy, but good for checking gmail etc. Since SplashVM is using GPL, if the vendor was following the GPL license I should be able to find the source on their website. It is possible to find some pieces on the Splashtop vendor website, but it is the responsibility of the system vendor not the subcontractor to make available the source for the actual firmware they are shipping. In this case, it matters to me for a couple of reasons. I wrote the driver for the Marvell Yukon-2 EC Ultra NIC's on this motherboard and would like to know if 1) the vendor fixed some bugs 2) the vendor still has some bugs that other users will pester me about. As copyright holder for this driver, I may have to go nasty to find out; stay tuned.