[Nyororin]

My, how this topic deviated from the original question...

I think Veespin has a point though. From the start, romaji was brought up as another form of writing Japanese. If you ask the average person in Japan what romaji means, they will tell you that it`s the transcription of Japanese sounds into the roman alphabet. NOT the use of the alphabet itself.

Yes, the roman alphabet is used often in abbreviations - such as MMM`s example (PC, DVD, etc)... But not romaji. You only ever really see romaji in use as a style aspect, or on public signs together with the regular Japanese. (Not just trains, every intersection is also labeled in romaji.

But used all together in a sentence or even a paragraph is pretty rare. There is no rule against it being done, and it is entirely possible... But people just don`t. It`s usually considered a pain to write something or read something in romaji. Try it with a local Japanese friend! Write a sentence in romaji and see how much they stumble reading it. Throw a random romaji word into a normal Japanese sentence and see how long it takes for them to realize that it`s even a Japanese word. There are no cases where a Japanese word written in romaji is easier to parse than it`s normal form, therefore no benefit to writing it in romaji. Language tends to take the path of least resistance, which is not that of romaji.

The Roman alphabet is indeed used in Japan to an extent, but not to the point where I`d consider it the 4th writing system.