Unfortunately I won't be back at Wacken in 2011 as have used up all my brownie points with the missus to get there in 2005, 2007 and 2010.
Definitely fly an Oz flag from your tent and be prepared for the locals to freak out when you tell them where you've come from, e.g. "Vot, you komm all ze vay from Hostralia?? Respect!!!!". They seem to think we come from the other side of the galaxy and not just a 24 hour flight.
You could always wear your flag as a cape but I just used me accent!!
[Tip for flag poles - we went to HOA the week before Wacken and scrounged some abandoned poles from the wreckage in the camp ground on the last day. Just gaffer taped 'em to our camper van at Wacken and had an instant flag pole!!]
Stumbled across truckloads of Aussies at HOA and WOA - in fact saw some of em last weekend at the Melbourne Overkill gig and the next day outside the Grand Final.
Also, if you're going to Wacken, have a look at the Hamburg Ballroom website for details of their Wacken after-party the Sunday after Wacken finishes - this year it was Mob Rules (awesome) and Stormwarrior (who had to pull out due to an injury to their drummer but Lars from Stormwarrior still turned up and was chatting to the punters, including us - a top bloke!)