Bottle-necking and diseconomies of scale....
Here's a not-particularly-good example of how diseconomies of scale can interfere with the practices of those who would abuse the network and transform it into something it was never supposed to be - a broadcast medium... The BBC News article Computer viruses face slow down (a couple of days old now) talks about how creating bottle-necks in the network can interfere with the spread of computer viruses. A virus is - I suppose I could argue - a weird entity that changes bits of the network into broadcast nodes, eventually bringing it all down as a direct consequence...

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