In a year and a half of playing BLM the only three times I've used surecast were when I was trying to improve and make use of less common spells like surecast. I purposely cast it and was confused when it didn't let my spell continue when I moved. Second time was figuring out what happened the first time. Third and last time was when I thought "Surely they didn't actually cripple this ability like this?" and saw that it really did still interrupt my spell when I moved.

Surecast is useless for most anything but pvp and perhaps a few healing situations.