Did you not see my links to where a ThinkPad, certified by Ubuntu, has broken screen brightness? I own an X140e and it has been a nightmare. I've had it for a year and I still can't get bluetooth to work[1]. I've also tried a Carbon X1 and it leaves much to be desired.
Like I said, it's a gamble. Sometimes the hardware and drivers and phase of the moon is right and everything works. Sometimes no amount of kernel flags and customized modules will fix it. I (along with many others) am willing to pay to not have to worry about potential problems.
The backlight issue is not a bug inherent to Thinkpads. The kernel works very hard to sort out the whole vendor specific mess about backlight interfaces and works out an appropriate place to manage the controls for users (what users? system daemons? console users? desktop environment? desktop end users?) There has been some major rework around kernel 3.16 and many behaviors have changed.
In the case of ThinkPads, you have three interfaces to control backlight brightness: acpi_video0 (standard ACPI interface), intel_backlight (GPU interface), and thinkpad_acpi (vendor specific interface) all with different semantics conforming to ACPI standard, Windows 7 behaviors, Windows 8 behaviors, and vendor private behaviors, and you have user interfaces including BIOS wired special keys, sysfs, udev, X utils, GPU control panels, and desktop environment settings to control the brightness. You have these moving parts for just one vendor and the kernel needs to coordinate all the madness with all the vendors. And the fixes coming out in latest version kernel might not even make it to your version of distros.
So there is a lot of complexity in the even seemingly trivial screen brightness control. Linux still has much to do with the support of heterogeneous hardware. But this is the price you pay for the freedom.
I haven't seen you mention it anywhere, so did you try a BIOS / firmware update? I've had similar bugs on multiple Thinkpads before and they were universally cured by an update.
I've tried 12.04LTS, 13.10, 14.04LTS, and now 14.10. Sometimes upgrading, sometimes from a clean install. The current issues with my ThinkPad are due to bugs in the latest drivers.
Like I said, it's a gamble. Sometimes the hardware and drivers and phase of the moon is right and everything works. Sometimes no amount of kernel flags and customized modules will fix it. I (along with many others) am willing to pay to not have to worry about potential problems.
1. I ranted a little about it near the end of a recent blog post: http://geoff.greer.fm/2015/01/03/ten-years-of-progress-in-la...