As to 1: it is in many ways insecure (though bound to be hacked might be a bit much.) While dropbox isn't technically a cloud based backup, it can be used that way and there was a period where a glitch left it totally exposed for about four hours ( http://en.wikipedia.org/wiki/Dropbox_(service)#Reception ). I actually love cloud based backup, but I encrypt my files before I send them and I am dealing with just my own personal data. A company with data they must legally protect would need to be wary.

As to 3: Personally, I love gmail. But from a corporate perspective, you can still exert more control over exchange. This can be significant, especially for highly regulated businesses that need to worry about frequent e-discovery and may perhaps wish to take steps to limit what is sent.