A few thoughts:
* This only works with Git. It doesn't look it'd be much work to make it work for all 4.
* This only pins deps you've declared; that set may or may not contain transitive deps. If it's not complete, the transitive deps will be frozen, forever, until you blow them out of your GOPATH.
* Issue #3 looks fun.
* Yeah, we use git internally, but we should definitely add support for other vcs when we can squeeze the time for it.
* True, I purposely kept this as simple as possible and forcing people to keep a complete Godeps file didn't sound like a terrible tradeoff (I actually like that it makes it that explicit).
* Issue #3 will have me scratching my head for quite some time, but I'll find a way!
Thanks so much for the feedback!