[ZeroAdunn]

Actually, they have yet to find a habitable planet excluding kobol. Remember earth like planets are pretty rare in the BSG verse. From what I understand the season finale will deal with the issue of finding a habitable planet and whether to settle down or not.

Of course, like renegade said, the cylon spies aboard are the problem. Is all it takes is for them to get a message out with the location of every planet the humans are on, and its orbital bombardment for the poor souls who aren't in the fleet.