You may not care, but I personally avoid SQS and Dynamo for lock-in purposes. I'd rather run my own systems and have the option of moving to GCE or something later.
I've found in the past that moving code between different queue and job coordination systems is pretty straightforward. Operationally of course you need to learn the new infrastructure but that is unrelated to fears about vendor lock-in.
Dynamo is more of a beef than SQS. I've found that Dynamo usage tends to grow. Like a fungus. Applying sufficient fire to remove it later seems beyond many shops' ability to marshal.
(Also, SQS is really weird about latency and places pretty ugly limits on responsiveness.)