I always do about a half mile on the treadmill or elliptical before I lift. I take the five minutes to find my playlist, untangle my earbuds, and mentally prepare myself for a great session. Nothing too much, but just break a quick sweat.
I see people doing some serious stretching for 20 minutes before they do anything. I have always read / heard to do a light warm up, but I do agree with the others as long as you are doing light weight warm ups. It is not necessary.
The key is to get blood into the muscle before you use it strenuously. However you go about it.
Obsessed is a word the lazy use to describe the dedicated