Logo Redesigns - Do they always work?

Over the past few years there have been many logo redesigns, from twitter to hotmail to microsoft office. But have they all been a success?  or have they flopped and gone pretty much unnoticed? Below are some examples of logo redesigns, which do you think have mad the service and company appear improved or better in some way? leave a comment and let us know.

A Redesign of the Google Mail Logo

Did anyone even know what hot mail was before the envelope redesign

redesign of logo service

redesign of logo, professional service

Twitter Logo Redesign

Virgin Atlantic Redesign

you don't have to change your logo

So which were the best, which failed, which impress and which don't? You tell me?

Also if you have a logo redesign to share, tweet @andykinsey