Most Polybcarbonate plastics contain Bisphenol A which migrates into any food or drink in contact with it without any heating (just repeated washing is enough for the Bisphenol to begin coming out of the plasticleeching). Its been known since the 30's that Bisphenol A behaves like the female hormone Estrogen but no-one in the plastics industry bothered thinking one further step ahead to work out what effect it may have on our babies!
www.latimes.com/news/nationworld/nation/la-na-plastics3aug03,0,234908.story?coll=la-home-cent er
Theres some daily dosages information on Wikipedia which is pretty scary (see the table on this page: en.wikipedia.org/wiki/Bisphenol_A )
The European Food Safety Authority study clearly shows using a Polycarbonate bottle significantly increases a babies exposure to Bisphenol A www.efsa.europa.eu/en/science/afc/afc_opinions/bisphenol_a.html
Lastly this is an American page but shows which manufacturers have Bisphenol A in their products - again it makes depressing reading with NONE of the bottles from major manufacturers like Avent being Bisphenol A free. zrecs.blogspot.com/2007/07/z-report-bisphenol-in-polycarbonate.html
Just look up Bisphenol A on Google - scary stuff - I'm replacing all our bottles today!