Interesting thread, when I was on the island of Borneo we experienced a fair amount of their use from the Iban tribesman, lovely people and deadly on monkeys with the blowpipe, the blowpipe is a part of their national symbol, like Australia has the boomerang. They were about 6 ft in length and made from bamboo and from memory the darts were made from bamboo slithers. The Iban tribesmen were, traditionally headhunters and are awesome bushmen, they used the blowpipe to great effect.
By the way, monkey is quiet nice.