In reply to John Newbiggin: I'm a bit biased but think they can be very good or they can be a waste of money.
Having worked on one over the last 4 winters and now running my own it's down to the individual client to make the most of them.
People from the courses have gone in a variety of directions, from many who don't work in the industry any more to one who's a successful MIA and WML.
Pick your course wisely though, some are better than others, some simply specialise more in certain areas.
Qualifications alone do not make a great instructor, on the right course you will get great input from quality, experienced instructors.