Foxconn, a company that makes, among other things, motherboards, makes and sells a motherboard that intentionally checks to see whether Linux is running on it and, if so, hands back broken ACPI (power management) information. This is especially interesting in view of a 1999 email from Bill Gates that turned up in anti-trust litigation, in which he proposes that ACPI be somehow made to work only on Windows.
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UPDATE: it turns out that several motherboard manufacturers have the AMI BIOS version that does this. Foxconn has released a test version that fixes all but a trivial error, and later will release a production version. I hope the others follow suit. Details on the Ubuntu forums.