I have used your mapping service to map my wordpress.com blog to a .org url.
Does this constitute redirection or is mapping something different?

Many thanks

However, I also want to understand whether mapping from old to a new domain has any constraints or whether I should re create my, as yet unpublished, content?

Thanks

Is there a restriction of 1 blog per account holder? (usually identified by their email address).

No there isn't. When we register a username account here the email address we provide becomes our unique identifier. When we are logged into WordPress.com and register a blog it's registered to that username account we are logged in under and to the email address which is our unique identifier. We can register as many blogs as we wish and provided we are using the same username account then all the blogs will be registered under it and the associated email account. We can change our "display name" but that display name will appear on all blogs registered under the same username account.
http://en.support.wordpress.com/email-address/
http://en.support.wordpress.com/change-your-username/#change-display-name-nickname

Is there a restriction of 1 blog per account holder? (usually identified by their email address). I want to open a second blog with a .org domain and transfer my .wordpress.com content to it - but only if the mapping process doesn't impose restrictions.

Otherwise I will incur the overhead of recreating the same content on the new domain before going public.

The alternative to this is for me to recreate my old .wordpress.com site (used as a development site without public contact) in the new .org site. A price I am prepared to pay if there are any inconveniences from the mapping route.