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.

Damn.

I use a Carbon X1 and have had no issue. Before I've been through other X's and a W.

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.

Very specific Chromebooks fit the bill as well. One that works particularly well is the Acer C720.

Edit: wanted to clarify that this C720 is my current personal portable. My other is a custom built desktop also running Ubuntu.