I think the US are a bit inconsistent by their half-mast flag flying, 30 days for a president is a bit excessive. Not sure what the rules are here in oz but in the UK it is just for the day of the funeral for all "important" people except the reigning soverign when it is from the death until the funeral.
I also believe that an individual can't fly the US flag at half-mast unless it is in response to a presedential or state governor proclamation.
However, there are other occaisions when flags are at half-mast - memorial day or something?