Using these modules and hooks in mkinitcpio.conf, under an ide-legacy installation, speeds up my boot times by two seconds.
MODULES="piix ide_disk ide-cd ext2"
There’s literally nothing there — and it works great. The initial image loads extremely fast and passes control to the kernel in a flash. That’s the way I like it.
So, for the record, this is a 1Ghz machine that boots from grub to login in 23 seconds. I have yet to shave some other things — like the modules, and the wait-to-once trick, but I don’t know how fast it will end up. And since ultimately it will probably autostart to X, it might actually go upward. But I’m OK with that.