The longest retreat I have attended is 4 days at the Blue Mountains Insight Meditation Centre. It was noble silence therefore no speaking although whilst doing our chores and washing up there was a few words exchanged. I'm theravadin buddhist.
I've also done the weekend retreats at Nan Tien Temple Wollongong which I love because they are short even though the buddhist teachings are Mahayana, so a bit different to my perspective. I really enjoyed the tai chi retreat they have.
I normally attend a meditation centre on a Wednesday night in Chippendale Sydney but with a new baby I've been absent for a few months now.
There is a Vipassana retreat in Blackheath that just focuses on Vipassana but I prefer the retreats that are buddhist focused.
In the end any meditation form is great huh? It's hard work too. I put some links here to my fave meditation centres and some links to some really good dhamma talks in case anybody is interested.
http://www.bswa.org/modules/mydownloads/ Look for talks by Ajahn Brahm - the funniest monk around
http://www.meditation.asn.au/ My fave retreat centre
http://www.bodhikusuma.com/metta/ My usual centre
Hope this inspires somebody!
Janelle