I am a big fan of John Wells' blog. He does know I exist unfortunately. My old email started spamming the world after I joined LinkedIn. Yes, I'm making excuses.
So anyway he frequently mentions Wikipedia as a source. This may be because he is more a descriptive phonologist than a prescriptive one. A smart choice and one which takes quite a bit more brains to pull off and is generally better for the world. The last thing we need is another British accent dictator.
Anyway while looking to see what they mention there as "general knowledge" on one topic the article on Japanese Learners of English popped up. It's great: well-researched and better referenced than the stuff I've written on the topic. Give it a read if you have a Japanese student. Send a note if you want a good resource for teaching it.
Here's the article: http://en.wikipedia.org/wiki/Japanese_speakers_learning_r_and_l