Confirming this as well... If you see this error, NetDB, Failed to fetch, etc., it is not any problem with your iDevice, Cydia, the jailbreak, or really anything at all. In fact, if you are seeing this right now on 2/4/2013, it most likely means everything is working properly!
The servers that provide the apps, the 'sources', are overloaded with people trying to download. Waiting until the servers are less loaded is the only solution, right now.