You are right, but actually these people are currently using IM and emails for the communication because communication is essential for the work they are doing. I want to move these to web and make them more personalized and customized to that particular community or company.

my startup is similar to socialcast, yammer, but my approach is different. I want to add more features and and some other socialnetworking stuff.

Gmail was written using Closure library built by google itself. Google release it for open source community now.

That is not proof, just another statement that means nothing without supporting data.

Also, if GMail is such a successful use case for Closure library, one could wonder why did they build Google Wave client with GWT?

I am playing with pyjamas currently. It is not working properly with chrome. I am trying to resolve that issue now.