This morning I mentioned to Jeff that one of the things I find odd in my spiffy new JPS Tanakh (given to me for Chanukah by my dear friend Cynthia -- no, not this one, the other one!) is that there are vowels printed beneath the Tetragrammaton. Yud-Heh-Vav-Heh (henceforth YHVH -- easier to type) is unpronounceable, so why add vowel markings to it? It turns out there's a reason for that, which leads to a funny historical note.
We generally substitute one of two names for the tetragrammaton: adonai or elohim. A Rabbinic custom developed, of adding vowels to the YHVH in some editions (e.g. not Torah scrolls, but study texts, the ones with vowels and cantillation markings). We take the vowels which would go under the letters of the substitute name, and put them under the YHVH. (With me so far?) That way, when one sees the tetragrammaton in a study text, one can glance at the vowels and know which substitute name was meant to be used.
And what would happen if you pronounced, phonetically, the tetragrammaton with the vowels for "Adonai"? You'd get Yehovah! Which leads to the amusing historical note: the name Jehovah is a mistransliteration of the tetragrammaton with "Adonai" vowels. Not knowing the Rabbinic custom of inserting the vowels of the substitute name beneath the letters of the unpronounceable Name, someone assumed that the thing to do was to read the letters with the vowels which were on the page, thereby creating the name Jehovah. Near as I can tell, that "someone" was a thirteenth-century Spanish Dominican monk named Raymundus Martini, in his 1270 C.E. work Pugeo Fidei.
This transliteration misunderstanding led, however indirectly, to the first religious argument I ever engaged in. At the age of eight, I got into a shouting match with our gardener (a devout Jehovah's Witness) about the name of God. Naturally enough, he insisted God's name was Jehovah; I, righteously indignant as only an eight-year-old can be, insisted it was Hashem. (Guess nobody had told me what "Hashem" actually means: "The Name." It's another workaround for the unpronounceability of YHVH.) Our housekeeper broke up the quarrel, horrified. Today I'd probably argue that the real problem was that we each believed we had the One True Answer; surely God has as many names as we can divine!