Should we advice clients to use Amazon Ec2 instances if any one asks for cloudhosting

[sumesh]

Normally many clients ask me whether he should switch to Amazon Ec2 thinking it is a premier one and some kind of magical hosting.  I know the cost is a large factor which I normally suggest them to consider before switching as many clients in the past who moved from normal VPS and dedicated server hosting ended up is giving more than double the cost earlier they used to pay to get the same level of server qualities and resources. 

Another issue is IP reputation, I saw more than 90 % of servers which I have set up in Amazon Ec2 ended up in Spam while mails are sent from these servers and I am not sure why they use the same IP ranges for those free servers which they used to give and also for the paid ones as well. 

So my question is, when and which cases I should suggest a Cloud hosting like AMAZON to a client  who ask me should he switch from VPS/dedicated to cloud ec2 instance