I was invited to the LBP2 beta, and got the DCUO beta as well. I've put more time in DCUO right now, though, as I never have the creativity and/or patience to make any levels in either LBP game, and I'm not one of those noobs who rip off other people's work unless they're ok with people copying it (so basically, stuff like templates, and maybe a walkthrough on making levels x_x)
You should have gotten two e-mails, the first one with a non functioning code in the body of the e-mail. But when you view the source code for that e-mail there is a second code that was to be the one that showed up (my opinion) but was not coded correctly. That hidden code would get you to the store and download the beta. Then Sony sent out a second e-mail with a new code that was active and let you download the Beta.
If you failed to get the e-mails make sure that you have Notifications turned on in your PSN Account or they will not send you e-mails...
Yeah I didn't get in the LBP2 beta so it must have been limited to a select group. You never know though, they may expand it out later and include all PS+ members. Didn't they do something similar with KZ3 beta?