I think he needs some time. Watching from the sidelines is no substitute for actually playing IMHO. He's got a quality running back, a proven receiver (Moulds) and some exciting young receivers with potential (Lee Evans, Josh Reed). In the games so far, he's had receivers in the open but has generally been overthrowing them, a sign of jitters I believe. Once he hits his stride and gets his timing right with his receivers, I think he'll be all right (if his o-line can give him more time to pass)
I think it's premature and unfair to compare him to Rob Johnson, who I admit is my most hated Bills QB ever.