TerraCoin doesn't really change anything in the bitcoin chain except for the block rate and diff retarget rate. I don't think it serves any useful purpose except as a pump n' dump scheme.
It doesn't matter if it gets 51%'d now or not, it'll be dead in a month due to merged mining anyway.
It's a pointless fork.
As far as I can see, all other coins excluding Bitcoin are flawed even more than Bitcoin itself. Unless something much better emerges,
having "backup" Bitcoin chain is good idea.
It's not a backup if it is subject to the same risks. That's why IMHO ppcoin is the only bitcoin alternative which adds value: It experiments with a different network security model.