Since there were no comments after my request for review for the patch that makes NetBSD be Multiboot-compliant, I have commited it to the tree. This feature is enabled as a default on i386's GENERIC and GENERIC_LAPTOP kernels; for others, you need to add options MULTIBOOT to their configuration file.
Please note that regular GRUB builds will not boot these new kernels properly. This is because of a bug in GRUB Legacy. You either need to install grub-0.97nb4 from pkgsrc or manually apply this patch to the GRUB sources.
See multiboot(8) for more information.
Edit (Feb 6th, 21:06): Some typos fixed based on comments from Reinhard von der Lippe. Does anyone remember seeing this happening (the post update) a couple of days ago? If you use an aggregator, you should have seen an update to the post that looked very similar to this. (More details on the comments.)