There really are a very limited number of tickets for Mix:UK remaining. I know because I'm having to set expectations with a lot of internal Microsoft folks who'd like to attend but we simply wont have space. (Usually we can squeeze a couple of extra folks in as long as the promise not to sit down or eat any lunch :-)).
Anyway, Ian's blogged about what we might (or might not) be doing in the way of give-aways for attendees. He's not revealing much but there are a few hints in there.