Nice post. I fully agree with you that using only the basic services (IaaS) from any Cloud provider will provide more resilient systems than using IaaS + SaaS (like ElastiCache, RDS, ELB). But I would also like to know why you would not consider Rackspace another type of vendor lock-in. Even though it supports multiple clouds, the customer would still depend on RS for features like autoscaling and new instance provisioning. Just for the records, I've used Rightscale for about a year, and I can say it is an excellent and powerful tool.