I did the Carmichael Time Trial workout on the trainer today. It was definitely a good workout. One of those workouts where after I'm done I have a little cough for about half hour because I've opened up some aveoli deep in my lungs that haven't used for awhile! The workout was an hour long so I'm patting myself on the back for finishing it. I normally ride my trainer 30-45 minutes max at a time.
I also have the Spinnerval 30 Minute Time Saver DVD. The Carmichael workout starts out with (after the warm up) sprinting intervals; 5 minutes on and 5 minutes off X3, as opposed to the shorter Spinnerval intervals that are a minute on and a minute off X12. One thing I liked about the Carmichael work out was that during the 5 minutes off they put in clips of Lance Armstrong and they interview the people doing the workout about the benefits they see from this particular workout. So you get a little "inspiration/motivation" along with the workout.