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Moz 1.8 has a newer Gecko than Firefox 1.0 - if you got a Firefox nightly, rendering would be the same. They're based on the same rendering engines, it's just that since the release cycles don't match, one will have a newer version at any given time. (When FF 1.1 comes out, it'll probably render better than the current stable Moz).
As for hype - well, Moz is huge, slow, ugly and unwieldy. That's why it never got any hype. Oh, and BTW, I don't know what I do different from you, but my mailto: works fine. Maybe I set it up somewhere and forgot.