Honestly, I think a lot of us are over-reacting.
Gunnar has played in net all his career, it's not as if he's going to be playing in goals for the first ever time against Villa. He knows how to dive, catch and kick, or else he wouldn't be a professional. It's not like FIFA/PES, were a keeper deemed worse than another fumbles the ball more and can't dive as far.
The only thing he lacks is experience, and to me, that just stands out as coming out for crosses, in which case, he seemed to have little trouble doing against Arsenal and in the reserve games I've seen.
I'm more concerned about the rest of the team. Just gotta turn up and peform.