WordPress.org

If you allow only Google Friend Connect users to login WordPress then:

1) Remove all logout links or replace them with the following one:

<a onclick="google.friendconnect.requestSignOut()" href="#"><?php _e('Sign out'); ?></a>

2) Remove all links to user profile. In case Google Friend Connect user will change his password plugin won't log him in after that.

If you allow both WordPress and Google Friend Connect users to login WordPress then your code should distinguish user type and generate logout and profile links appropriately. Here is an example:

<?php
    _e('Logged in as ');
    // Do not add link to profile and logout link in case of GFC user
    global $gfc_userdata;
    if ( ! isset($gfc_userdata) ) {
    echo '<a href="' . get_option('siteurl') . '/wp-admin/profile.php">' . $user_identity . '</a>. ';
    echo '<a href="' . wp_logout_url(get_permalink()) . '" title="' . __('Log out of this account') . '">' . __('Logout ') . '&raquo;</a>';
    } else {
    echo $user_identity . '. ';
    echo '<a href="#" onClick="google.friendconnect.requestSignOut()" title="' . __('Log out of this account') . '">' . __('Logout ') . '&raquo;</a>';
    }
    ?>

By default plugin adds Sign In button (or user's profile data in case he/she is already signed in) under comment form. Alternatively you may use following template tag to do this:

<?php if (function_exists('gfc_profile')) {gfc_profile();} ?>

Best place to put it is under comment form or "You must be logged in..." line in your comments.php