I have personally heard, first hand, of people being busted this way. They receive a slip in the mail box, then when they go to collect they are arrested. The police are actually waiting at the Post office.
I can't comment on any other countries but in Australia I have never heard of this being done. It is hard to believe that they would have a bunch of cops staking out the post office from 9am to 5pm for possibly a month or more just on the off chance that the person the package was addressed to might come in to pick it up. Even if they did grab you trying to pick the package up you could still say you didn't know anything illegal was in the package and hadn't even opened it yet. When customs seize drug packages in Australia it is generally not followed up for over a month and controlled deliveries are an extremely rare occurrence.
It is also standard police procedure in Australia not to let post office staff in on the details of any drugs investigations, as the staff could be involved themselves. I have spoken to people who work in Auspost who have confirmed that postal workers have been arrested for drug importation rings before and police will always factor this possibility in while investigating.
This is misinformation.
I know of someone in AUSTRALIA who was caught by undercover police waiting at a post office for at least 3 days.. And catching the person when he picked up the package.
And how can you say you didn't know what was in the package, when you are picking up something from an address that is not yours?
I'm not trying to scare anyone, I hate fear mongering.. But I think everyone should know the risks involved. I very much doubt they would go to this effort for personal amounts, but if you have a drop that has multiple no-shows, this should be at least in the back of your mind.