Dell XPS 13 (9333)
This page is a work in progress.
Installation largely runs smoothly. See below for potential problems.
Booting the install media
Booting from the install media runs with no issues. I had some issues with the cord of my external optical drive functioning weirdly, but I suspect it's specific to my device.
By default, this computer comes with an MBR with all four partitions already used. Additionally, I have read that if you delete any of the partitions, the boot process will break. (I can confirm this, although for obvious reasons, I only tested it once.) Therefore, a dual-boot with Windows is impossible on this machine, although just Arch would probably be fine. One solution could be booting from a permanent USB installation. However, that has its caveats too. See the next section.
BIOS and USB keys
Unfortunately, if you install to a USB key and select GPT instead of an MBR, the BIOS will fail to boot with "operation system not found", even of you use the hack where you set the boot flag in the protective MBR.
So far I have tried upgrading the BIOS, which did nothing. I still have more experiments to run before I conclude that this configuration is impossible.
On a stock install, the screen brightness does not work. When you use the function keys, the change is recognized by the system (if you have an indicator or something for brightness it will change), but this will have zero effect on the actual screen brightness.
For completeness, this issue is also present in Ubuntu, where there's a hardware enablement kernel specifically for this laptop.
You could try installingAUR. I haven't tested this yet.
Apparently there's issues with the trackpad, but I haven't tested it yet. The situation around this is is the exact same as the screen brightness: it's also present in Ubuntu, where it's fixed by the hardware enablement kernel; tryAUR.