The plugin copy/paste feature was discontinued with the introduction of server roles. Server roles are more powerful solution to the bulk server management problem.
Click "Roles" in the top nav. Roles should match the functionality of your servers. Most accounts have a database role, an application role, etc. Populate your roles with servers, but don't add plugin templates just yet -- you'll probably want to organize your existing plugins into roles, per step (2).
Since your account started out without roles, you'll need to take steps to organize your existing plugins into roles
Click onto a role, then click "gather plugins for this role." If there are similar plugins across all the servers in the role, you can add all those plugins to the role in one click. Once a plugin is assigned to a role, you can manage the plugin and its triggers in unison across all the role's servers.
You don't have to organize all your plugins into roles; you can leave some as individual plugins on a server. However, to fully take advantage of roles, you probably want to place as many plugins into roles as possible.
Previously, you had to generate a unique key for each server in your account (or use cloud keys). Now, you have just one account-wide key, which you'll see on the "add server" page after conversion. You'll see instructions for the Chef recipe and Puppet module there as well.
In April 2013, we transitioned from using server-specific keys to identify servers to a single, account-wide key.
Yes. Pingdom server monitor fetches server by the account key and hostname, and since the hostname hasn't changed, the same plugins will be fetched.
I'm transitioning to roles from an old-style account. Do I need to change the PSM key on my existing servers?
You don't need to change anything. Your existing servers will continue to report data with their legacy keys. However, for new servers added to your account, you'll need to use the new account key.
No, but you can achieve the same effect by specifying any unique string with the --hostname flag. As long as the string you supply is unique, the server will always retain its identity in PSM, regardless of any underlying hostname changes.
Cloud keys were discontinued with the introduction of server roles. Server roles are a better, more flexible solution to the bulk server management problem. They also save accounts money by not using a server instance as a template.