Very interesting podcast from the BBC discussed plagiocephaly, and talked in support of the pillows and against the helmets.
Its worth a listen (Start from minutes 18:40): 

http://www.bbc.co.uk/podcasts/series/medmatters
MM: IH: Sars like virus, Heartburn, Baby helmets, Tue, 25 Sep 12
(available as a download and through itunes)

Read also:

 

• Why Parents Should Know About Flat Head Syndrome
• 10 Points To Consider Before You Buy A Baby Pillow - Safe and Effective for Baby Flat Head!
• Why Mimos Baby Pillow? (Safe and Effective for plagiocephaly)
• Lilla Kuddis vs Mimos Baby Pillow