I joined up and am about to take advantage of the deductions on my tax return this year.
I think it is a good way of helping out a charity without having to sign up for one of those make-a-donation-once-a-month direct debit deals or buying raffle tickets. I help a chairty, they give me a good deal on my phone calls, I get to claim more back on tax and when I call their customer service I get to speak to someone in Australia.
The website is www.khacomms.org.au if you want to check it out.