Donins... all those requirements that people was adhere to are stated in a contract or buyer's agreement form(s). The underwriters of EBAy-I think it is Goldman Sachs- probably bought a few shares before offering them to their account holders. After that, they sell to the public. Of this offering of EBAy, I surmise that there weren't much left to offer to the public! Thus, the IPO is the official date where all the public can participate.
A month? Yes... To keep the stock from falling below IPO levels... or just to keep it at the 40-53 levels. Thus, not much selling is taking place while lots of buying is taking place.
Can people short sell now? I am not sure. You should be able to do it. Talk to your broker about it. If you are using a discount broker, phone them up. They must have a REAL broker that are willing to take your calls. Just tell them that you are interested in short selling EBAY shares first. Then... they'll talk to you :).