Found this interesting little article that should forever answear this question. Excerpt below.

http://www.b737.org.uk/iceandrain.htm


Rain Repellent
The rain repellent has been removed due to worries about the environmental effects of the "RainBoe" fluid used as it contains CFC's. It is also poisonous and in 1991 Boeing added D-limonine which has a strong smell of orange peel into RainBoe so that leakage could be detected. There are no plans to replace the rain repellent with another liquid product even though there are safe alternatives eg "Le Bozec".

On 25 May 1982, a 737-200Adv (PP-SMY) was written off by a heavy landing in a rainstorm. One report stated that "The pilots misuse of rain repellent caused an optical illusion".

Since early 1994 all Boeing aircraft have been built with Surface Seal coated glass from PPG Industries which has a hydrophobic coating. The coating does deteriorate with time depending upon wiper use and windscreen cleaning methods etc, but can be re-applied.