I thought my account had gotten hacked. All my guilds and friends were gone. Then, I logged out... logged back on... logged out again... and finally they showed up. Logged in a new character, now they're gone again.
Same thing was happening after one of the earlier big patches a couple of months ago (February I think?). Don't worry, they are still there, they just take a long time to load. Presumably the server potatoes are overloaded.