I don't invest based on what other people do. Institutional buying in particular has never meant much to me. Unless I know why they are buying and what their track record is, to me it's not any different than anyone else who is long. Warren Buffett is the richest man in the world and he makes mistakes, so these guys can, too.
I'll add that institutional buyers tend to use groupthink. Most were caught up in the sub-prime mess.