Considering buying a DS or a PSP to help alleviate the tedium of that flight to Japan? Well if so you had better not fly with a Japanese airline because both systems, along with any other device which emits a wireless signal are now banned outright on planes owned by Japanese companies.
More specifically, if the wireless transmitter in the device cannot be disabled then it is now illegal to use it, so Laptops and iPods are fine, whereas the DS isn't. Oddly enough, the PSP does have a wireless on/off switch, unlike the DS so we assume the blanket ban on all wireless enabled games devices is to avoid any claims of discrimination.
Wireless mice for laptops are also disallowed now along with headphones not supplied by the airline (no, I don't understand that one either), although previously banned items such as electric razors and calculators are now OK to use. Riyad will probably be annoyed when he returns from CEATEC though.
The reasoning behind the change in the law is being put down to the risk of electronic interference with control systems which, according to testing by Japan's transport ministry, poses the genuine possibility of disrupting a plane's control systems. While this may be a case of overbearing 'better safe than sorry' mentality, I have to concede: 30,000 feet in the air is exactly the kind of place I want to see that attitude. Whether it will catch on in any other countries remains to be seen.