FreeBSD 10 gpart cannot create boot disks for Intel Atom D510MO, neither
semi-automatic using bsdinstall, nor manually using gpart directly. I
have tried this on internal IDE and AHCI hard disks, and using USB memory
sticks. Nothing boots.

By only overwriting a partition scheme created by gpart from FreeBSD 10
with gpart from FreeBSD 9 using exactly the same partition parameters
(sizes and positions), and using /boot/pmbr and /boot/gptboot from FreeBSD
9, the disk or memstick is suddenly bootable with said Intel Atom board.

Fix: 

When manually overwriting the GPT 10 partition on said failing ada0 with
gpart from a FreeBSD 9 installer, using exactly the same partition parameters,
and placing /boot/pmbr and /boot/gptboot from FreeBSD 9 on the freebsd-boot
partition -- no further installation is needed -- only the disk partition
was manipulated, the said disk boots fine on said machine.
How-To-Repeat: 1. Install FreeBSD 10 from the scratch on a Intel Atom D510MO machine,
using "FreeBSD-10.0-RELEASE-amd64-memstick.img".

2. Let the BSD installer apply the default GPT/UFS formatting scheme to
the internal hard disk ada0, and complete the installation (which runs
smoothly).

3. Power down the machine, remove the memstick, and start it up again.

The Intel Atom D510MO board does not recognize the internal HD as a boot
disk, the disk LED is flashing for half of a second, and then the board
drops immediately into PXE boot (last in the boot sequence), since no
other boot media is present.