During cleaning, I lost the small (~.25" dia) mouthpiece o-ring. I couldn't find it, and I ran the CF without it.
Without the mouthpiece o-ring, a little bit of outside air is introduced just below the mouthpiece, which decreased draw resistance by nearly 50% and keeps the vapor/mouthpiece cooler during use. A side affect of using the CF sans o-ring is that the mouthpiece has a more definitive snap into place when extended, which I like. I don't get quite as big clouds, but I still get the same amount of total vapor from the CF. I haven't noticed any change in the location/amount of residue buildup.
I ended up finding the small o-ring behind the kitchen sink the next day, but I've left it off since then. I actually prefer the experience without that little o-ring. Your mileage may vary, but if you prefer a little more airflow and slightly cooler vapor, you should try it.