The most recent research by Dr. Daniel Klem, who has been studying the problem of bird/window collisions since the 1990s, has just been published in the June 2009 Wilson Bulletin. It is available, along with lots of other bird/window resources, at his website here.
Klem, Daniel, Jr. 2009. Preventing Bird-Window Collisions. The Wilson Journal of Ornithology 121:314 –321