[nemik]

This here is right on.

I will add that if you can afford the time and effort to do so, it would be good to design your system in the beginning to work on multiple providers without many issues. That means trying as hard as you can to use as little provider-specific things as you can (RDS, DynamoDB, SQS, BigTable, etc). In most cases, pjlegato's 1) will still apply.

But you get a massive side-benefit (main benefit, I think) in cost. There are huge bidding wars between providers and if you're a startup and know how to play them off each other, you could even get away with not having to pay hosting costs for years. GC, AWS, Azure, Rackspace, Aliyun, etc, etc are all fighting for your business. If you've done the work to be provider-agnostic, you could switch between them with much less effort and reap the savings.