You probably know Yifan Lu from his work on Vita/3DS/Amazon Kindle and various devices. He says you should register for Playstation Mobile, if I were you I would do what he says.
Sony declared PSM is shutting down about 2 months ago. The shutdown takes place in steps, final date for registration is May 31, 2015.
As the registration is free, you have nothing to lose for registering before this date. Also don’t forget to setup your Vita. Yifan Lu says it would be wise for a Vita owner to register and run a sample demo even if he/she isn’t a developer. Well, I follow Yifan Lu’s work from Kindle days and value his opinions so I can advise you to do the same.
I don’t want to speculate about it so I will leave it to you what you might regret about if you don’t register [Note from wololo: oh, oh, let me do the speculation, please! Here it goes: It’s pretty obvious to me that there’s something big coming up from a hacking perspective, and people who don’t follow the steps below might regret it for a long time].
Here are the steps you should do, quoted from Yifan Lu’s blog.
Once everything is installed, play with a demo! For example, BallMazeDemo is pretty fun. Before the demo will run though, you have to generate an app key. Refer to PSM’s documentations for that.
Update: notice the “after you get approved” bit. To get approved for a PSM publisher license, you need to go to to the PSM Dev portal, and click on the “Apply for PSM Publisher license”. You will be asked to provide full information, including an address and a phone number. Do not do anything on your PS Vita (including updating it) before you have received this approval. You won’t be able to even run a PSM game prior to this approval.