Seriously, I didn't bother signing up more than once. I signed up once, and even if I get into the Beta, I may not even participate in it. It's basically working for free, and unless you're really really into this game and/or have lots of free time, I don't think its worth it.
It's also basically getting to play a game for free?
Yeah you do have a point that you get to play a game for free. But at the same time, you will most likely have to spend a lot of time writing detailed bug reports. In addition, any work you've done to build up your character will be deleted when the Beta is over. I'd rather spend some $$ and buy a game that is already completed, so I can avoid having to write up bug reports, and also avoid having all my stuff deleted after about 3 months.
Another reason to play the Beta is to try get inside knowledge, so that you can get a head start when the retail version comes out. But to me it's just not worth being an elitist in this type of thing. There will still be hundreds of Japanese players way ahead of you anyway. In addition, I just don't have that much time to spend playing games, so I would never be able to keep up.