Registration for the open beta in the US closes at 4PM Pacific time today. If you miss it, however, don't be too sad. There'll be other chances to get a key, what with USA Today handing out a load of them, starting on Tuesday. No doubt other media outlets will get their hands on them too.
If you get your hand on a code make sure you use it before 5pm October 29th. At that time the download servers will be turned off. At one minute to midnight on October 30th the gameplay servers will be switched off and the beta will effectively end. After that you'll have only a few days to wait before the full game releases. Maybe you could use the time to replay Resistance 1 in preparation.