For us (ours is only 19 months and not very verbal so take with a grain of salt), we let the temper tantrum part last about 20-30 seconds. Not ignoring, but not reacting. Then I pick him up and speak calmly to him and comfort him as much as possible.
He had the negative experience to teach him that what he did was wrong, but I don't really want to let it go further than that. It usually takes about 5-10 minutes to calm him down after I pick him up. He can't be distracted from a thought once he's had it though, so it's more about him coming to grips with the fact that he can't do what he wants and he needs to express that disappointment.
Hopefully this will give him the skills to deal with disappointment later. Fingers crossed.
