I've seen it a few times. The last time was in January when I was in London for a protest. A friend and I decided to take a load of photo's of the tourist spots and of course some of us with big ben was top of the list. Going home on the train that day however I managed...
Watch to the end, I've just always liked this video...can't stop grinning. :D ;)
I have seen the actual...massive clock...in person. It was quite impressive.