Drawbacks for me:
Cold weather = stalling at startup. I just got used to giving it just a little gas to help 'er out the first 20 seconds or so.
Possible midrange power loss, along with a slightly more abrupt transition when the secondaries open up.
But it was worth it to get rid of the stupid throttle hang. Now the throttle response is MUCH better.
Play with the hole diameter. You might want to have a cold-weather (bigger diameter) and warm-weather (smaller) plug. Once the plugs are drilled out, it takes 2 minutes to replace (literally).
Remember, you can always remove the plug if you don't like it.
Enjoy!
