Gmail's fast new windows --only downside was that they closed when the main Gmail window closed. Google said that "If you're using latest version of Google Chrome, you can now continue to work in popped out windows after you close your main window. […]our friends on the Chrome team made it possible to transfer the code that runs Gmail from one window to another as the window closes. When the window that hosts the code fires an unload event, we move the iframe with the code to a surviving window. Everything continues to run, including timers and outstanding requests," expaind Google.
The feature is part of HTML5, so it should be implemented in other browsers as well. Gmail doesn't have tabs, but you can open many views in a new window by shift-clicking on a link, by clicking on "new window" icon or link. This way, you can keep a conversation open while composing a message (shift-click on "Compose mail" or Shift+c), open Gmail search results in new windows (shift-click on the results), reply to a message in a new window (shift-click on "Reply" or Shift+r).