To answer #273: While I don't own a U90 (U100 here), when I checked the bios to check the version, the system info said "Msi Wind U90/U100". To me this indicates that the two systems are synonymous as far as the bios goes. If I owned a U90 I'd try it, but I can't give you any guarantees of course.
I can also confirm that updating the BIOS partially fixed the issue (I have the same 5 levels of brightness thing and concur with the idea that we've migrated to this bug: https:/ /bugs.launchpad .net/ubuntu/ +source/ linux/+ bug/257827
To answer #273: While I don't own a U90 (U100 here), when I checked the bios to check the version, the system info said "Msi Wind U90/U100". To me this indicates that the two systems are synonymous as far as the bios goes. If I owned a U90 I'd try it, but I can't give you any guarantees of course.