I just hope Anet are smart/care enough to get peoples MAC addresses with the DxDiag scan (basically scanning and sending your hardware parts unique serial numbers).
Sure people can sign up with different hardware, but that is nearly not as common as using multiple emails or a proxy.
In a public beta where everyone has the chance on testing the game there should be an equal chance of getting in, and scanning for MAC addresses is one way to do it (and as I said I hope Anet does this as it's pretty straightforward).