Gmail, the Web mail service operated by search engine Google, could be gearing up for its official launch, as people using the service have found recently that the number of invitations they can send out has increased from four to 50. Gmail, which was launched in April 2004 and is still officially in a testing phase, is not open to the general public. At first, Google let only select family and friends open accounts at Gmail. But it has slowly opened up membership more broadly to friends o...