When you set up your Google Profile, you can select the information that is visible to anyone who views your profile. That includes what contact information you want to make available. You can choose to show an email address, a phone number, a mailing address, various screen names and more — and you can limit exactly who can see that information. It is not automatically made public. Instead, you can choose groups among your contacts in Gmail to provide information to.
You can also allow people who see your profile but aren't in your Google contacts to send you email, without giving them your email address. Google Profiles offers a tool, which you can enable by checking a box while filling out your profile, which allows for contact through Google Profiles. You can change your contact settings at any time.