Amazon recently announced that they are giving away a free micro instance to new accounts on their EC2 service. They call it their free usage tier.
So what is a micro instance then? Well, its their smallest computing unit in Amazon's cloud service. Basically, fire up one of these bad boys and you have your own little virtual server that exists somewhere in Amazon's vast computing nebulous.
What can you do it with it? Anything you want really. But most people will probably run linux on it and set up a LAMP (linux, apache, mysql, php) server to run web sites / applications.
What kind of experience do I need? Unfortunately, you need some skills to use Amazon's cloud services, its like running your own server with a little added complication.
I have found that micro instances are decent for most small to medium websites and testing. However, they can be a little underpowered especially with memory because they only have 630 something megabytes of RAM.
But who can complain with free? Existing customers like me I guess who the deal doesn't extend to.
More information on Amazon's EC2 free usage tier.