You mean like foo.bar@mail.com? Mine does too (most gmail addys do), and it worked. It did say my email address was invalid, but focusing and unfocusing the textbox fixed it. I don't think it's an issue with the email format, just the form is buggy.
Unless it has changed recently, Gmail ignores the dots anyway. So if you find a form that wont validate your john.smith@gmail.com, you can use johnsmith@gmail.com and still receive it.
