Having built a non-trivial production system, I have a love-hate relationship with AWS. I love the possibilities and potential, but I'm deeply disappointed when it fails to live up to the hype.
It's just a matter of alternatives. There's frankly no other IaaS out there that can match the features of EC2 (eg, EBS, elastic IP). These guys are unstoppable, they come out with more features every week.
Not the original poster, but here's some stuff I really wish AWS had:
a) Ability to map an elastic IP to an ELB. The CNAME thing it uses now has way too many drawbacks [1].
b) Ability to make an RDS instance a slave to or a master for a normal MySQL instance. This would make it possible to use RDS as a backup to our ordinary DB infrastructure using normal MySQL replication (and eventually, vice versa)
c) Retention periods for EBS snapshots. You can get this yourself by writing a few simple scripts, but it would be really nice if snapshots could simply be labelled "delete after 90 days".
d) A cross-availability zone, synchronously replicated EBS volume. This is probably fairly specific to our use case, but it would be neat if AWS natively provided something like DRBD.
It's not me in particular, but if you read the EC2 forum going back to 2006 people have been asking for full virtualization, multiple IPs, multicast, non-NAT, reverse ARP, shared EBS, etc.
It's just a matter of alternatives. There's frankly no other IaaS out there that can match the features of EC2 (eg, EBS, elastic IP). These guys are unstoppable, they come out with more features every week.