www.newscientist.com reports this week about a research project on Pirahã language numerals.
Hunter-gatherers from the Pirahã tribe, whose language only contains words for the numbers one and two, were unable to reliably tell the difference between four objects placed in a row and five in the same configuration, revealed the study../ [a.k.a. slashdot] responded with a lively discussion.
For more interesting stuff about Pirahã check Dan Everett's page.
Mark Liberman at Language Log has a point of view with which I agree. I don't think it's the language that determines the cognitive capacity. I think the cognitive capacity is independent of language as well as physical capacity is independent of hair color.