Solution plugins and the holy pluginregistrationtool
From now on after registering plugin with pluginregistertiontool, It's no longer needed for moving plugins between environment. Plugins and their steps can be included in solutions.
For best practice register all plugins to the sandbox and database, otherwise you might have problem moving them to other enviroments (ONLINE for example)
The pluginregistretiontool is still important and necessary for the first registretion of the plugins to the MSCRM 2011. It is still imposiable to do it from the CRM web application.