How long should a Channel Trailer be?

I think a channel trailer should be short and to the point, make sure to include what your channel is about and make it interesting and too long so I would say 40 seconds to 1 minute!
Most channel trailers I have seen are between 1:00 and 2:00 minutes. It's true that if it's shorter, then there is a greater chance that people will watch the whole thing, but what good does that do if then you can't really get across what your channel is about and show cast your skills. If you keep it around 1:30 it should be short enough for most people to watch it.
I'd echo what everyone else here has said. Not necessarily the shorter the better, but 45-60 seconds seems to be ideal as long as you cram your best work (and what you're most proud of!) into it. Show people what you've got and just have fun with it, don't think too much and people will appreciate it. :)