Hurray! It's about time they announced something; goodness knows how long they've already been talking and working together. Glad to see Roger hung on in and managed to persuade him.
Sounds like a good move to me. From reports of today's match, Roger was trying out a lot of serve and volley (with varying degrees of success). Fortunately for him, Ferrer was missing a lot of the passing shots. He'll no doubt adjust his game quite a lot to play against Rusedski on Wednesday. It's good to see him trying s&v more as it makes him more aggressive and means he has yet another option on the court.
By the way, I don't think Roger would consider Gilbert for his coach. What could he bring to Federer's game? He's hardly a technical coach. And whilst I don't know either of them personally, I would very much doubt that those two personalities would get on.
Annacone would be a better choice than Gilbert imo, but Tim Henman's only 30, enjoying the best years of his career with Paul and not looking to give up any time soon.