When booting a .hddimg on atom-pc from a USB stick, it hangs on "waiting for removable media...". Removing and re-inserting the USB stick doesn't help.
Maybe you could try to downgrade the udev for 164 or so and check if it happens? So we might have a more clear view if it is a kernel issue or an udev issue.
Ok, this was due to me having meta-oe in the build at the same time, and meta-oe's udev took precedence and subsequently broke everything.