I have started my 4weeks CELTA a week ago, if I hadn't had to pay 940 pound upfront I would have left that course from the second day.
I had to teach for 20 minutes on the second day! I was petrified. The amount of paper work is horrendous! It could be that I have other priorities to deal with though.
There is a book all about the celta course, it's called:
success on your certificate course in English language teaching.
Do note that the course is very good, and teaching ESOL learners is by far my best ever experience. So I say if you are up for a challenge and have no priorities whilst doing your CELTA, then go for it :)