Sony's PlayStation Now streaming service is scheduled to go into private beta at the end of this month, and the company has begun sending out invites to its lucky participants. For the first wave, Sony seems to be focusing on testing Now on the PlayStation 3 console. A thread at NeoGAF seems to confirm that only PS3 owners are seeing invites at this time. As for how Sony's choosing its beta testers, that's not entirely clear.
After PlayStation Now was announced, Sony posted a website where gamers could sign up for more information — though it never specified that invites would be distributed this way. Some NeoGAF users seem to be receiving invites at random, though most if not all of them are current PlayStation Plus subscribers. To see if you're in, check your email for a message with the subject: "You are invited to participate in the PlayStation Now Private Beta." If not, don't fret; it's likely that Sony will keep expanding the beta before Now launches publicly this summer.