Urgent Query on Australian Citizenship-HELP!!

[Anna Schmidt]

I am a German Citizen, who studied at UNSW for 2 years. I really enjoyed my time at UNSW (2008 - 2010) and hence applied for PR and am returning back to Australia in this July.

I intend to stay in Australia from July 2012 for atleast 4 years, and then apply for Australian Citizenship.

Currently the Citizenship website states that One needs to reside in Australia on a valid Australian visa for 4 years "immediately" before applying.

My Questions are:

1. What does the word "immediately" imply in this context, they certainly don't mean that I cannot leave Australia for 4 straight years? Do they?
2. If I go for Vacations, or visit back to Berlin, would that be an issue?
3. *MOST IMPORTANT* - Would this requirement of 4 year residency change again (like it changed from 2 years to 4 years in 2007?). How often do the Citizenship rules change?

Thanks,
Anna Schmidt