Two articles about it, starting with
Mushroom or Muffin, Rem Koolhaas's helium-filled "Non-Pavilion" for the Serpentine Gallery in London
link -
http://www.hughpearman.com/2006/22.html

photo by Hugh Pearman
A speech bubble for London
By Edwin Heathcote
Published: July 4 2006 18:00 | Last updated: July 4 2006 18:00
(in Financial Times)
"Architecture," Rem Koolhaas once said, "is lethally slow." In his latest building, just completed in London's sylvan Kensington Gardens, Koolhaas has made an almighty effort to speed it up with an extraordinary balloon, constructed in super-quick time, tethered to the grass and sheltering a translucent structure below. This is the new Serpentine Pavilion, a temporary building to sit beside the eponymous gallery, commissioned each year by its director Julia Peyton-Jones from an important architect who has yet to build in the UK. Those featured include Zaha Hadid, Daniel Libeskind, Oscar Niemeyer and Alvaro Siza.
The new building evokes a thousand metaphors, from the hot air of interminable architectural theory to Chaplin's great dictator toying with the globe, from Renaissance domes to the enduring visionary idiocy of future worlds sustained in great bubbles on alien surfaces. And they are all appropriate.
Link for rest of article --
http://www.ft.com/cms/s/f0bfca52-0b7c-11db-b97f-0000779e2340.html
I found these articles via the online newsletter for architectural news from archnewsnow.com.