Warm up, it's worth it.

The warm up.
Something that many exercisers leave out of their routine.
Many feel like it's a pain. They don't have that added time. They don't see the benefit. Too good for the warm up, huh? Well, let me tell you why I think you're wrong.

Warming up DOES...
increase your heart rate
increase the blood and oxygen flow to your muscles (prepping them for the workout to come, and making them work more efficiently once warm)
increase range of motion in your joints
help avoid injuries such as muscle tears and pulls
helps with mental preparation
ultimately, enhance performance (more blood going to the muscles = better performance)

Warming up SHOULD...
be about 3-5 minutes long
warm up the muscles you'll be using while exercising
i.e. If you are running, walk for a good warm up. If you are going to be lifting the elliptical gets your arms and legs warm.
be at a lower intensity than your workout, the point here is to prep the muscles. That is why it's a warm up.
get you to a point where you're breaking a light sweat

Warming up CAN BE...
walking on the treadmill, increased to a slow jog
a low setting on the elliptical
jogging in place
a few intervals on a recumbent or spinning bike
Jumping Jacks
etc.

Trust me, from someone who's been injured. Injury prevention is FAR better than injury recuperation. It's worth the 5 minutes it may take to prime your muscles...after all you're still burning calories!

It's also been asked if stretching should be involved in the warm-up routine. I would recommend you stretch after your workout when you're muscles are at their warmest point. This will help to increase your flexibility.