Just exactly how good is aerogel?

I've come across mentions of aerogel insulation a few times recently - it featured in a few of the buildings from the Solar Decathlon that I wrote about in the current issue of Construct Ireland. The claims made about it are generally impressive: that it's an ultra-light, extremely high performance translucent insulator that was, apparently, developed by Nasa. But I have no real way to verify these claims, so I'm curious to hear what readers know about it. I've certainly yet to see it used in a project in Ireland.

A new article on Jetson Green certainly speaks fondly of the stuff: 

Despite the fact that we are now living in the 21st century, aerogel insulation seems like a material out of science-fiction. It is the lightest solid known, although by volume it is 99% air. It is breathable, but it doesn't absorb water. It is incredibly strong for its weight. But most importantly, it is a fantastic insulator.

There's also an interesting discussion about it on greenbuildingforum.co.uk. 

Anyone know any more?