Personally I couldn't give a rat's behind, and I say '10' | 'X' depending on which way the wind is blowing (yes, really).
I don't know. Some people argue that it's called '10' because that's a natural progression from 8, 9... which is not true.
Before Mac OS X, we used Mac OS 9, NOT Mac OS IX.
So it's clear that Apple were trying to tie into the whole 'generation X' use of X, which is 'cool'. Hence, although they've said that it should be pronounced 'OS 10', it's ambiguous. If it's 'OS ten', then why not write it 'OS 10'? Why 'OS X'? Since when did we all start counting in roman numerals once we reach X, er, ten?
Let's see, they could have done it in hex, and we could be on 'OS A', or perhaps binary, so that would be 'OS 00001011', "but pronounced 'OS Ten'".
It used to be that movie sequels were billed as 'II', 'IV', etc., but now they're sticking with Arabic numerals, ala 'Spiderman 2'. Why is that? Are people getting dumber?