mine got changed at the 40k service (car's done 37k miles tho) 
got told the original air filter doesn't need changing till 60k tho!  
 
i was shocked by that. the nice chick on reception (one reason i still go back to my dealer for servicing lol) offered to have it done if i wanted to tho. 
maybe it needs cleaning to get me those extra ponies revo promised!