In addition to Ed's point about slower repetitions being a crucial part of weight training properly, I'd like to comment on something that [i]can[/i] work for everybody, no matter what your goals.  

As "buzz words", you hear about two things inparticular these days that are effective one way or another: circuit training, and slow, prolonged workouts (ala Ed's post).  The former for improving your cardiovascular endurance, and the latter for burning more calories per workout session.  But since these activities, in respect to time, seem like direct opposites to each other...which one is right for you?  The answer: [b]BOTH[/b].  Circuit training is concentrated on time [i]between[/i] workout sets, while a prolonged day at the gym simply stresses doing the actual [i]workout repititions[/i] slower and more focused.  

Remember, your heart rate doesn't need to be going a mile a minute (like you're running a 10mph pace) to get a decent cardio workout!  After doing slow, steady exercises repeatedly, my heart feels like its pumping at about the pace of, say...a brisk jog.  And that's sufficient!  Spending +/- 1 minute per set, with 30 seconds in between sets and occasional 1 minute breaks usually puts my workout at around 55 minutes per day.  And at a heart rate of ~130bpm throughout the entire routine, that's like jogging at a 7mph pace for an hour!  

This routine covers ALL of your bases:  proper strength training, cardiovascular/muscle endurance, increased fat burning potential, and less likely chances of injury (like, say, [i]tearing your tricep[/i] [;)]) as a result of slower, steadier repititions.  The greatest benefit?  No matter what muscle group, weight vs. reps, or mass gain vs. fat loss plan you're on, this plan can be incorporated into all of them with equal benefits to your short- and long-term health.

I thought he used slow in reference to each rep, not the entire work-out.  The point behind moving the weights slowly is to make each rep more effective by keeping you from using momentum, not to improve endurance.  That's the job of 20 rep squats [:)].  Most of the guys I've seen sling weights do a bunch of sets and spend more time at the gym than the guys who do one more effective slow set.z

Correct, that's what I meant.  My term should have been "slower repetitions", not "slower workout".  [b]In effect[/b], it becomes a slower workout, and in turn - a greater cardiovascular push.