I tend to think that the hygiene hypothesis is true. Nothing Lamarckian about it, just environmental effects on the immune system.
I stand corrected regarding invoking Lamarck in this case. It will be very interesting to see what will come out of more controlled studies such as the one you suggest.
I'm also curious about why I'm not tormented by allergies continually since I have two cats (which I'm allergic to on a skin test). I read something saying that this could lead to such high levels of IgG that the allergen is all grabbed and pulled out before the IgE can get into the action. I'm rather curious about this but information is hard to come by.