It was triggered by the marketing announcement of a microwave based one, which was deemed a really poor alternative to the others. But the discussion itself has a lot of good info on water heater technology.

[link|http://science.slashdot.org/article.pl?sid=05/11/25/0413215&threshold=1&tid=126&tid=14|http://science.slash...=1&tid=126&tid=14]