I'm probably going to be the only person from higher leagues saying this, but I think 2-3 can be used effectively. In the right circumstances.
Note that in saying this, I haven't used 2-3 zone for a very long time, and probably wont for a while yet. I see it as a last resort tactic.
I actually think the main benefit with 2-3 zone is the rebounding boost. Despite it being a defensive tactic, I find one gets a large amount of offensive rebounding from it. If you have a high IS rating, you can get a lot of easy putbacks from it.
That said, you can get torched from the outside from it. One has to be confident that the team you are playing will play inside, and that your PG and SG have enough defense to be able to cover the opposition guard comfortably.
Its very much a desperation tactic though. LI and and an outside offense is just silly, but it can be effective occasionally with an inside offense.
For an example where 2-3 worked well, this game is a good example. http://www.buzzerbeater.com/match/13043/boxscore.aspx
We were comfortably outclassed against China in this game, but the 2-3 zone rebounding advantage almost got us over the line.