Hi, it’s me who wrote a blog entry about One Parent One Language.
http://wenjonggal.wordpress.com/2010/02/05/one-person-one-language-and-other-theories-that-bug-me/
Frankly, I said as a single parent who is bilingual with English my dominant language, and learning Mandarin, and wanting to do three languages with my son, One Parent One Language is just… impossible. I am not going to raise my son to be a monolingual anglophone because I am a single mom. My parents are thousands of miles away, and in any case, they don’t speak some interesting minority language: they are monolingual anglophones like most of North America. And I certainly don’t have the money for a nanny several days a week.
My son started daycare in French (the majority language here in Quebec, but I wouldn’t say the dominant language in that most of our friends are anglophone, english radio, tv, books and all other media are readily available, and most things like packaging are bilingual: French is present but so is English) when he was three years old, and goes now 2-3 times a week. So he gets French immersion there, but for the first year he only replied in English.
So, basically, I read books in English and in French. I put on French and Mandarin cds and dvds. I speak English to him but also French… more often French outside the home as people in the park, stores etc are majority francophone and I want to help contribute to the French atmosphere and not run around speaking English in public with my son.
There is no way I could speak “only one language: don’t mix the languages while talking†esp in Mandarin. I teach him French words while speaking English, and translate French while I’m speaking it into English if there is a word or ten he doesn’t know. And in Mandarin I integrate new words we are learning into games and everyday speech. Every language I know I learned that way… definitely almost all teaching materials and language classes are conducted in more than one language… adding in more and more of the second language into the mix as more vocab, sentence structure and understanding is accumulated.
I certainly haven’t found it has “mixed him up  he has a noted preference for English since it is our home language, and it is so available in the outside world, but he can tell you what language any word or sentence is. Anyways, it is normal for anyone who is multilingual to “code mix†ie use words from another language if they don’t have the word for it in the language they are speaking: In Quebec even unilingual anglophones say “dépanneurâ€, “cafe au lait†and “croissantâ€.
So, while some parents might have two parents with two languages they are fluent in, OPOL might work as well as any other method, but for some of us it is just not a possibility and without it we are doing just fine.
Here is a great article on Raising Bilingual Children by the Linguistic Society of America:
http://www.lsadc.org/info/ling-faqs-biling_child.cfm