According to this Gmail FAQ,
Gmail doesn’t recognize dots (.) as characters within a username. This way, you can add and remove dots to your username for desired address variations.
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If you created your account with a dot in your username and you wish you hadn’t, you can change your ‘Reply-to address.’
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Please note that to log in to Gmail, you must enter any dots that were originally defined as part of your Gmail username.
My gmail id is sandipb. By Gmail’s policy, that makes the sandipb@… email address, the same as the sandip.b@… email address. In fact, theoretically, I should even be able to use s.a.n.d.i.p.b@… as my gmail address.
So why, oh why, does Gmail allow new distinct accounts to be created with dots in the same name, when the same name without dots is also registered???
So there is this poor bloke, who registered a gmail address as sandip.b@…, and now his mails keep coming to me, including communications with his bank! 
They tout it as a feature. But I see it as a major hole in their user account system, which is non-intuitive and inherently flawed. The fact that Google account is dot-sensitive and gmail is not, seems like a major bug which needs to be highlighted more.
