Check out this. (http://www.nihongoperapera.com/psn/register-sony-japan-account.html)

Why should I do it?
- Apparently a friend of mine says you can download demos (if you can figure out which are the demos) and play them on your PS3 and PSP.

Will game demos that I download work on my US PS3?
- So far I've downloaded one demo for my PS3 and it works. I haven't tried a PSP demo yet. I will tell you if it works or not.

You can get demos on the Asian accounts too. And some demos actually allow you to upgrade to the full version with just a small unlock file download (Bejeweled 2 and Star Trek DAC for the PS3 are two games that're like that).

For other demos tho, i.e. LBP, well, 1GB download, and if you like it, you need to buy the disc :/

Took a whole frigging day to download the LBP demo. Because I needed to shut down my PS3 for 10 mins after every 30 mins or so of downloading.

Wait a minute, the US PSN store doesn't have demos?

The US store has demos, but I'm more interested in the JP market rather than the US. JP has a lot of PSX games (for 600 yen) than what the US has currently (I'm really thinking of getting Magical Drop III).