You may have noticed this recent entry in the Gmail Blog http://gmailblog.blogspot.com/2010/09/turn-off-gmails-conversation-view.html:
What happens to your Iconix icons if you elect to use turn off Gmail’s conversation view? The icons will continue to work in both conversation viewing modes. So, you can pick either conversation viewing mode and you will have icons to give you visual information identifying the senders. The personal icons from 
, our person icon service, will also display in both viewing modes.
Conversation View On Conversation View Off
You can also toggle between the modes if you so desire and our icons will continue to work. You can find what you want in the view you prefer.