I have been talking to some colleagues about how to start a project that you know it will probably need to scale in a couple of months, think of a heavy text content site. [update: like a lyrics site with kind of social features added to it, with urls that makes the search engines happy]
Actually what we have as far as I know are services like google appengine, that provides you with a full api where you can build your web site. You know they give you processor time, storage space in their datastore, kind of non-relational ( but scalable ) database and a lot of network throughput. What I like about this service is that you pay very little money for a lot of resources, at least as far as know.
Then you have virtualization services like linode and amazon ec2 and other services that I like more because it gives you full control of how to program your site without limiting you with a closed api or closed vendeor.
Microsoft also offer public cloud computing services called azure and I think yahoo also.
But here are some things to have in mind. I don't have a good feeling about who's the real owner of your application since you upload your code to google appengine for example. Or then you fear that they'll say you that your application violates some policies you were supposed to follow. Well, I think you understand.
I think comparing services like appengine and the ones that offer virtualization creates you another problem if for any reason you need to move from one to another, because you probably will need to re-enginer the urls if you'll change the way you are programing and you know, there goes all your page ranking and you'll have broken links if you gained some of them before wanting to move your application.
I am sorry if my English is irritating you, but this is as far as I can talk, what I want to know from you is what will be your thoughts on this topic. What will be the service you'll choose and why. Which services are you using and what is your experience in it.