Feet - both.
There was an increase in the informal vote, probably of about 1.5-2%, but not as much as some people would have you believe - the western Sydney seats which had informal votes in double figures have very high informal votes at every election, partly because NSW has optional preferential voting at state level (as does Queensland) and people get confused because just voting '1' is OK in state elections but not in federal ones. For the numbers nerds out there (and I know there's quite a few of you), this is analysed in some detail at blogs.crikey.com.au/pollytics
Off a sample of one - my booth - there were 27 informal votes (out of about 1000), of which 8 were mistakes and 19 were blank or intentionally spoiled (including one which made an anatomically challenging suggestion towards the Prime Minister). This is par for the course. There were no donkey votes in my booth.