results of pinyin tests

browser	text	place	no charset	no charset or css	UTF-8	Big5	ISO-8859-1
IE5	Chinese	table
	Chinese	regular	good	good	broken	good	broken
	pinyin	table	good	moving don't work, others good	good	good	good
	pinyin	regular	good	moving don't work; others uneven baseline	good	good	good
NN4	Chinese	table
	Chinese	regular	good	good	broken	good	good
	pinyin	table	only 2nd and fourth OK; all moving broken	only 2nd and fourth OK; all moving broken	only 2nd and fourth OK; all moving broken	broken	only 2nd and fourth OK; all moving broken
	pinyin	regular	broken	broken	broken	broken	broken
Mozilla	Chinese	table
	Chinese	regular	buggy in <p> but broken in zh-TW span	buggy in <p> but broken in zh-TW span	buggy	buggy	buggy
	pinyin	table	good, except for moving i's and u-umlauts		good, except for moving i's and u-umlauts	good, except for moving i's and u-umlauts	good, except for moving i's and u-umlauts
	pinyin	regular	good, except for moving i's and u-umlauts		good, except for moving i's and u-umlauts	good, except for moving i's and u-umlauts	good, except for moving i's and u-umlauts

The problem listed with i's and u-umlauts in the moving diacritics is that with i's the tone mark seems to extend only to the edge of the normal character. And since a sans-serif i is thin, there's no way to distinguish the marks from each other, or even from just the regular dot on the i. The problem with u-umlauts in moving diacritics is that the tone mark doesn't move up high enough, and overwrites the umlaut.