I've read a few reports on them being loose, I always wanted an original Air but I know they were extremely fragile so I never bothered. However the new Air is really temping me but the few things I've read on the hinges is still worrying me slightly. Can anyone give me the low down and how they actually are? Are they all loose? Just a small number? I think I read somewhere the 13" had stiffer hinges, is this true? Thanks.