Bruce Moore, editor of the forthcoming second edition of the Australian National Dictionary, has an interesting discussion of a classic Australianism at Ozwords:
Mate is one of those words that is used widely in Englishes other than Australian English, and yet has a special resonance in Australia. Although it had a very detailed entry in the first edition of the Oxford English Dictionary (the letter M was completed 1904–8), the Australian National Dictionary (AND) included mate in its first edition of 1988, thus marking it as an Australianism. A revision of the OED entry for mate was posted online in December 2009, as part of the new third edition, and this gives us the opportunity to test the extent to which the word can be regarded as Australian. Not one of the standard presently-used senses of mate in OED is marked Australian. What are they doing to our Australian word? […]
The AND definition differs slightly from the OED one: ‘a mode of address implying equality and goodwill; frequently used to a casual acquaintance and, especially in recent use, ironic.’ Examples of the ‘ironic’ usage include: (1953) ‘I’ll remember you, mate. You’ll keep!’; (1957) ‘I’ve just been sweating on an opportunity to do you a damage, mate.’ The quotations chosen to illustrate the OED entry do not include this ironic, and sometimes hostile, use of the term. This range of usage with the primarily positive mate is analogous to the range of usage with the primarily negative term bastard in Australia. Bastard is mainly used in a derogatory way, as it is in all Englishes, but in Australia it can also be used in a good-humoured and even affectionate way. Sidney Baker captured the range of meaning when he wrote in 1943: ‘You are in a pub knocking back a few after work and being earbashed by a mate. At length he reaches the point he has been rambling round so long and, after a pause, you (the bashee) say: “You’re not a bad old bastard—for a bastard!”’
There’s a lot more there (the post is excerpted from his book What’s their Story? A History of Australian Words); it’s lexicography at its finest.