I don't think they do it that way here. It is more a question of available resources - if a particular server is under more load than others, they will either move sites around or add more servers as needed. Speed has not been an issue for me in the two years I've had sites hosted here.
There is no specific uptime guarantee that I'm aware of, but my experience has been excellent thus far. Over the two years I've been here, I'd say that the total amount of downtime was just a few hours (WAY better than 99%).
Simon Jessey | Keystone Websites
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