I have been using nitrous oxide on and off for about 3 years. I first heard about it from my friends, and purchased 2 24 packs online. I was conservative at first, waiting maybe 5 minutes between balloons. As I inhaled the sweet gas, it gave me a slight numbing feeling mixed with a warmth all over my body, and the usual warbling in sounds.
That was three years ago. I try as hard as I can not to order it very often, since I've heard that extremely heavy use can cause a b12 deficiency and nerve problems. I don't order a 24 pack or 2 anymore... my last purchase was a case of 360. If I go to have a quick balloon after school or work, it quickly turns into 5 balloons, and before I know it, I'm waking up surrounded by dozens of empties.
The feeling is incredible, but it's impossible for me to control myself. I've reached a plateau with nitrous that I never would have thought was possible. I usually do straight cartridges until I can't... just going from balloon to balloon, trying to just breath in the sweet nitrous without letting any air in the way. I feel a warmth all over my body, and it gets to the point where I can't even move anymore... I'll just lay on my bed panting, desperately needing to get some sleep.
While the feeling is incredible, it's very difficult to control. If I ever end up in the same room as a tank, I wouldn't survive the night. Nitrous can be dangerously addictive. It sucks being a nitrous head.