I installed macOS HighSierra on the MacBook Pro 13": 2.4 GHz, 512GB SSD, 16GB (hey, it’s my daughter’s laptop, so it’s fair game as the guinea pig).
The installation process converts the boot drive to APFS as advertised (no choice, no asking for permission, which I deem yet another manifestation of disrespect for users).
So far, I see no performance benefits whatsoever, only weird performance problems.
Can you say “performance downgrade”? Emptying the trash is glacially slow; trash containing 1000 files should take a second or two, but took about 90 seconds. This is the SSD performance boost we’ve been promised that comes from APFS?