Comment 2 for bug 784937

Just some more data, collected from oneiric builds of 20110601 (Ubuntu 2.6.39-3.10-virtual 2.6.39)

i386-t1.micro:
 block-device-mapping: {'ami': '/dev/sda1', 'ephemeral0': '/dev/sdb', 'root': '/dev/sda1'}
 /proc/partitions: xvde1

i386-m1.small-ebs:
 block-device-mapping: {'ami': '/dev/sda1', 'ephemeral0': '/dev/sda2', 'root': '/dev/sda1', 'swap': 'sda3'}
 /proc/partitions: xvde1 xvde2 xvde3

i386-m1.small-instance:
 block-device-mapping: {'ami': 'sda1', 'ephemeral0': 'sda2', 'root': '/dev/sda1', 'swap': 'sda3'}
 /proc/partitions: xvde1 xvde2 xvde3

amd64-m1.large-ebs:
 block-device-mapping: {'ami': '/dev/sda1', 'ephemeral0': '/dev/sdb', 'root': '/dev/sda1'}
 /proc/partitions: xvde1 xvdf

amd64-m1.large-instance:
 block-device-mapping: {'ami': 'sda1', 'ephemeral0': 'sdb', 'ephemeral1': 'sdc', 'root': '/dev/sda1'}
 /proc/partitions: xvde1 xvdf xvdg

So, it looks like basically the kernel is starting its enumerating with xvde.