The advanced Postgres datatypes are pretty much my favorite thing in the world. We use HStore internally all over the place, as well as some more exciting projects that we haven't said too much about yet. As I mentioned elsewhere in the thread, if you're interested in trying out some of those extensions, contact me directly.
I am curious as to whether you do pro-rated pricing?
Ronin = Small Instance: 1.7 GB of memory, 1 EC2 Compute Unit (1 virtual core with 1 EC2 Compute Unit), 160 GB of local instance storage, 32-bit platform. ~$60/month spot.
Fugu = High-CPU Medium Instance: 1.7 GB of memory, 5 EC2 Compute Units (2 virtual cores with 2.5 EC2 Compute Units each), 350 GB of local instance storage, 32-bit platform. ~$120/month spot.
Ikea = Large Instance: 7.5 GB of memory, 4 EC2 Compute Units (2 virtual cores with 2 EC2 Compute Units each), 850 GB of local instance storage, 64-bit platform. ~$240 / month spot.
Zilla = High-Memory Extra Large Instance: 17.1 GB memory, 6.5 ECU (2 virtual cores with 3.25 EC2 Compute Units each), 420 GB of local instance storage, 64-bit platform. ~$360/month spot.
Baku = High-Memory Double Extra Large Instance: 34.2 GB of memory, 13 EC2 Compute Units (4 virtual cores with 3.25 EC2 Compute Units each), 850 GB of local instance storage, 64-bit platform. ~$720/month spot.
Mecha = High-Memory Quadruple Extra Large Instance: 68.4 GB of memory, 26 EC2 Compute Units (8 virtual cores with 3.25 EC2 Compute Units each), 1690 GB of local instance storage, 64-bit platform. ~$1440/month spot.
I think Heroku will pay less than the spot price for the raw server, but fork out bandwidth, storage, EBS IO, backups and so on. Amazon sells its basic servers cheap, but virtually nothing is included.
It looks like their margins go up at Zilla, but maybe the high-RAM instances need more bandwidth and backups.
It's not clear from the pricing page, and I'm assuming it's per month, in which case it's reasonable, especially given the value added services being offered, especially the ability to fork the database and the automated creation of read slaves.
It looks like a solid offering. It's probably not right for companies that are subject to HIPAA or PCI compliance requirements, and there's no information on the use of compiled extensions in the db which may limit it's utility if you're wanting to use PostGIS or other specialist datatypes.