Currently the primary place I use to look for plugins is WP-Plugins.net. It is updated several times a day as plugin authors use it as the first place to announce their plugins. They also have a feed which you can subscribe to.
The new plugins directory is actually an interface to WP-Plugins.org which for years has served as a hosting place for several plugins. I too have few of my plugins hosted out there, but stopped maintaining them because I couldn’t track their downloads and it also meant another place to upload.
Another problem was that I had to maintain a separate folder that I would use for development so that I could SVN to wp-plugins.org.
The new plugin directory however gives an impetus to plugin authors to once again start hosting out there. Users can rate and comment on your plugins, you can let WordPress take care of your hosting and not bother with hosting them yourself. It will also serve as a good place to get your plugin out.
However, on the downside, it could also result in a totally mismanaged unit like the Themes Directory.
My very best to the WordPress team on the launch. It will definitely go a long way to centralize WordPress development.
As for me, I’m going to continue hosting my plugins on my own blog, atleast until I see fit.