Matthew Garrett has written a new article summarizing the state of UEFI/SecureBoot on Linux. Overall, the situation isn't good if you're using hardware from one of three major vendors.
Aside from the Linux UEFI issue that can brick Samsung laptops
(well, he does go over that issue in greater detail and there's now a workaround in the mainline kernel), Garrett's post also points out issues for Toshiba and Lenovo hardware too.
Matthew Garrett says some Toshiba PCs won't boot Linux since they managed to leave the signing key out of the database used to validate binaries as well as the signature database signing key used for whitelist/blacklist updates. This fortunately is in violation of Microsoft's Windows 8 certification guidelines so an updated UEFI/BIOS will likely be issued for the affected hardware by Toshiba.
Some Lenovo PCs will only boot Windows or Red Hat Enterprise Linux. This situation is more concerning and Matthew just says, "I recommend drinking, because as far as I know they haven't actually got around to doing anything useful about this yet."
Aside from the Toshiba, Samsung, and Lenovo problems, UEFI/SecureBoot isn't doing too bad on Linux at the moment. Read more details in Matthew's blog post
While not related to SecureBoot, while talking about less than stellar hardware vendors with Linux support, Gigabyte recommends using Microsoft Windows
. Also see my 2012 Linux hardware shopping guide