The news coming from the observatory this morning now that people have been able to return to the site is that that all of the telescope buildings are intact, as are most of the other structures, however the Lodge (on site accommodation for visiting astronomers and other staff on night shifts), the AAO Director's Cottage, a small storage shed and two homes on the mountain have been destroyed. The mains power lines are down and the site is now on generator power. Soot and debris have entered a number of telescope buildings and it's possible some of the smaller ones may have heat damage. A lot to clean up is required but at the moment it is thought that the observatory will be back in business in about two weeks.
The damage could have been a lot worse and the main reason it wasn't is that the people running the observatory are not, in fact, stupid (regardless of what WatAWorld thinks). The observatory does ensure no tress or shrubs grow close to any building and performs regular controlled Hazard Reduction burns in the run up to summer every year. The buildings themselves are fire hardened to various degrees, e.g. ember screens fitted to windows. Lessons were learnt from the complete destruction of the Mount Stromlo Observatory in Canberra in bush fires in 2003, the fact that a major bush fire was able to pass through the Siding Spring Observatory without a single telescope burning down is testament to that.
The NSW Rural Fire Service also deserve credit for their tireless efforts fighting this and the other 170 odd fires currently burning in the state. They've posted photos of the aftermath of the fire at the observatory on their Facebook page, here: http://www.facebook.com/media/set/?set=a.10151382336805552.525957.213250965551&type=1
There also a story with good photos and video from the ABC here: http://www.abc.net.au/news/2013-01-14/homes-destroyed-in-nsw-bushfire/4463136