Copying keys and certificates to another one Mac for iPhone development

Import by selecting the private key from the keys tab. This prompts a password and after the password it saves in .p12 format and you can install in all the systems.

You should be able to export all your provisioning profiles with all the keys (Public and Private) with just one export

In the Organiser under the Devices tab, you need to select Developer Identity and export that to a file and give it a password. Move that file to the new system and import it into Xcode and your full identity will be set up

Import/Export works differently in Xcode 5+. This Apple Developer guide shows you how to do it.

Your account is shown under Xcode → Preferences → Accounts, and can be exported by clicking the gear icon () in the lower-left.