Submit handler for the login form. Load $user object and perform standard login tasks. The user is then redirected to the My Account page. Setting the destination in the query string overrides the redirect.
function user_login_form_submit($form, &$form_state) {
global $user;
$user = user_load($form_state['uid']);
$form_state['redirect'] = 'user/' . $user->uid;
user_login_finalize($form_state);
}