Four weeks leave is standard in Australia. It is quite common for people to take it all at once especially if they want to travel overseas. Australia is so far from the rest of the world that to go overseas can take a day or more of travelling each way. I agree with IceDread that a longer (complete!) break from work is better and you do feel recharged when you go back. I find that I only really start to unwind about 4-5 days into a holiday so longer is definitely better for me!

Cheers,