I'd happily give Hernandez more game time, but I wouldn't drop Rooney from a regualry starting place with Berbatov. I'd bring him on earlier or give him the occasional start. He played rubbish yesterday but he was out of position for most of the game. Also you have to remember that even though he didn't score, he was fantastic against Birmingham and has been creeping towards good for for a couple of games. Just ignore last night as a bad day and see how he is the next time he plays. He's still a top player, just needs to get the run of consistent good form and a couple of goals.
I wouldn't be suprised if Hernandez starts on Saturaday though.