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http://www.webfaction.com/services/hosting?affiliate=apeternelli they have good support team, low prices and a well balance between easy-to-use and do-everything-you-want.

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By the way :

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- Engine Yard and Amazon Ec2 are Clud Hostings, Amazon EC2 is better but complex, EY is expensive.

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My Advice ? Go for something easier like webfaction, they are not on the cloud but they are good for your first experience they give you a ready to go rails/passenger server, and the option to install everythig you want (i have a entire user account, you can even compile from source)

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- Unicorn and Passenger are ruby servers, they work in combo with Nginx (mostly)

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- Mongrel was a nice ruby server, but now it is out of date (2008 if i recall)

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- Capistrano is a tool to automate maintenance, deploy and other task on one or more servers, it is usefull so you write settings and procedures only once (im not an expert so i can't be very clear about it)

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it is very usefull, but i recomend to watch it later. By the way other similar tools ar Puppet and Chef

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How to select a host? *

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Depends on your needs!
My advice ? Go for the cheaper, make some experience and then change to a
serious one!

Do I need unix knowlodge?
It is recomended to know something about *nix !

How to deploy?
How to maintain?
I am missing the point ...

How suitable are the more "automatic" hosts such as Heroku for a web app?
Very much!!! If you are serious and can afford them, go for them!!!