I'd say I'm usually fine with about 5-6 minutes of a warm-up, NOT including a stretch: I agree that static stretches should be saved for the end of the workout (after a sufficient cooldown). I prefer ROM moves and dynamic stretches. Joint mobility exercises are also excellent, especially before kettlebells or weight work.
How much of a warm-up one 'needs' is very individual, depending on such things as age, fitness level, what you've been doing (ie: if you've been sitting around watching a movie, you'd need more time to get everything lubed up than if you just came home from shopping and walking around the mall, for example). Also, it depends on the type of workout. A high-impact, intense workout needs a longer warm-up, IMO, because you are going to be taking the body from '0 to 50' instead of '0 to 20' on some level of intensity.
For my outdoor walks, I walk for about 2-3 minutes at a warm-up pace, then do dynamic moves (leg swings, 'hurdler' leg circles, kickbacks, etc) as a warm-up.
I really hate it when some instructors (Gunnar Peterson is one, Michael Olajide is another) do a 'stretch AS warm-up'. For those, I always substitute dynamic moves.
I usually prefer longer warm-ups for several reasons:
1) My joints feel much better during the workout if they are well warmed (one purpose of the warm-ups is to get sinovial fluid lubricating the joints)
2) one can always skip to the next chapter when one is warmed up enough for their own wants or needs, but if only a short warm-up is provided, there's not an easy recourse (repeating it is boring, using another workout as a warm-up can be inconvenient) so I like it when instructors provide long warm-ups rather than short ones. This makes it work for everyone (those who like shorter warm-ups can just skip ahead).
Shorter warm-ups work well, though, in some workouts where the initial segments are intentionally lower in intensity, or there is a gradually increasing intensity.
I really like the long warm-up in Cardio Kicks, for example (and I sometimes use these longer, 10-12 minute cardio warm-ups before weight work).
