Ok, so here's my take on it. Anyone correct me if I'm wrong, or if it's specific to my computer:
1) when booting the live CD, it flickers through several login stages. It briefly shows a mint@mint command prompt, then it also shows gdm for about 5 seconds (long enough that I wondered if I was meant to login).
2) the new usplash theme looks VERY professional, it's gorgeous, as is the new gdm (but I don't like that it hides the mint logo (though this was raised in another thread)
3) personally, I don't like dark themes, but the one labelled Linux Mint is very nice.
4) flash works better than ever, it no longer wams my cpu usage up to 100%
5) did I mention how professional it looks
EDIT: yep, I also remember noticing the ubuntu start-up music (only on live CD, not after install) as gus points out below.
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