Lefty, I've thought about this a lot, too. My father was Icelandic and my mother Thai, and I learned Thai by association (not immersion, since my mother spoke English to me) as a kid... I wouldn't say I am fluent, but I can understand a lot and speak conversationally. My father died before I was born so I never was exposed to Icelandic. What ended up happening is that English became my #1 tongue, with Thai falling far behind as I got further into school (after age 5 it went downhilll quick). I had to go to Iceland at age 22 and live there for a year, immersion + classes, to learn the language from scratch. I spent two semesters at a Thai language school a couple of years ago, to try and improve my skills. Basically though, I wish I hadn't been allowed to speak English at home.. it would have saved me a LOT of grief later in life, especially for communicating with grandparents, for example. Imagine never sharing a common language with your own grandparents...
Anyway, not to say that I am dissuaded from cross-linguistic parenting as a result. Ktspktsp speaks Arabic, French, and English fluently (he learned them all as a kid), so we have five languages between us. If we have kids, I'd like for them to learn at least conversational bits of all of those languages... language-a-day would work well for all of us, actually! (Since I need to learn Arabic and French, and ktspktsp needs to learn Thai and Icelandic). To me it would be really fun... and would keep us learning together, as a family.
Of course, the main issue is where the kids are raised. I am not sure yet if I want my kids raised in one country (particularly the US)... it would be great to rotate them through the five countries that we are a part of... then they would be immersed in the school and socialization of all five. That would be truly multicultural, and beautiful, to me.
