Well I went to watch it yesterday (Wednesday 17th). In the UK that was the premiere date.
I must say that I am impressed. It has more battle scenes than part II (The Two Towers), and it had us laughing and crying .(Well I did shed a tear at one pouint

)
Thank god I had booked the superior seat, otherwise it would have been really uncomfortable! Everyone enjoyed it (I am presuming that we were all great Tolkien fans - most of us had booked the seats as early as December 3rd!). We clapped (and I must admit I don't often tend to do that at the cinema).
Unfortunately my idea of finishing the Return of the King book didn't come to light, but I hope to finish it and watch it at the cinemas again soon.
Watch it in the cinema whilst you can!
saj