Not knocking the tremendous work Martin has done maintaining and extending the Installer, but the GPT handling in 9.x/-current did seem a bit confusing to me. It could be just me and my understanding, but the last time I tried it there seemed to be a disconnect between the way an MBR disk is set up and the way it’s done with GPT. Being used to the MBR setup I was looking for a similar setup with GPT.
What I thought I saw was that with MBR partitioning one selected the disk, then defined or redefined the partitions. This seemed to be true regardless of what type of previous MBR partitioning was done on the disk. (Although a previous MBR setup for a non-NetBSD system on the disk sometimes caused problems.) With GPT, at least on a disk that already has some GPT wedges, it seems one selects GPT wedges to “partition”, not the disk. At least it seemed to me that all the existing GPT wedges were displayed and I don’t recall seeing an option that allowed me to select the raw disk and define or redefine the GPT partitions on it. Not sure about the UEFI or BIOS booting as I do that manually on my installs, but I know Martin did fix some issues that I was originally having with that.
