Ever wanted to find out more about GetUp!? If so, they don't make it easy. The first place I normally go when I want to know something about an organisation is their annual report.
It took a bit to find their annual reports - Google is your friend in the end.
Although the front page of their web site says they are a "movement of 579,343 Australians", the most recent annual report with published numbers is from 2008/09. Page 2 of that report says that as of July 1, 2009 they had 312,875 members.
Frankly, I'm amazed that for an organisation that is so big on disclosure that they haven't put out their 2009/10 annual report yet - and I would have thought that their 2010/11 report couldn't be very far away either.
If you ask me, if you want to be counted as a member of something, you have to pay to join. GetUp! is being sneaky in saying that they have 312,875 members - in 2008/09, only 17,295 individuals actually paid GetUp! money. Many of them must have given a few times, as there were 31,095 donations in total. $96 per donor, of $53 per donation on average.
What they'd be more correct is to say that they have 312,875 on their mailing list (collected over a variety of campaigns), and 17,295 "members".
But that's just me.