My problem isn't so much about what is appropriate (anyone involved in the science faculty will know that pretty much anything goes as far as dress standards) but more about what I can wear without looking like I'm some sort of elitist. When I first met my supervisor he was wearing jeans and an untucked, short-sleeved button up with lots of miniature pictures of The Beatles (in multi-colour) on it. While I'm sure he would be dressed differently had there been some sort of meeting schelduled, it looked as if this was his 'standard' work outfit.
Ideally, I would like to wear trousers, dress shoes, button ups with a sportcoat and the occasional tie but the last thing I want to do is make my supervisor/colleagues feel under-dressed and end up resenting me because of it. I'm a bit older than your typical intern (26) and my supervisor seems like a really nice guy but it's hard to say how he (and the other post-docs etc) would react to 'the new guy' wearing more formal clothes.
Any general advise/experiences (especially from Aussies in the field) would be greatly appreciated.