From what I'm seeing, if your root disk is on EBS and your SSH keys are there, you cannot SSH into those hosts right now.
Also, the availability zones are disparate in terms of what they can support. A great number of my instances are in 1d because of unavailability in others.
Note that the region-1[a b c d & such] designations are randomized per account; my us-east-1d won't (necessarily) be the same as yours or anyone else's.
Also, the availability zones are disparate in terms of what they can support. A great number of my instances are in 1d because of unavailability in others.