Opera 11 Alpha is available for testing, Extensions is one of the exciting new features in the Opera 11 alpha. Extentions allows you to add new functionality to Opera. Right now about 15 Opera extensions available for testing from the Opera Extensions archive.
Along with the Extentions there are updates of opera mail with drag items support, personal bar is replaced by new bookmark bar to allow quick access to faviorite bookmarks. Now the plug-ins can be loaded when they are required , which will speed up the loading of the sites, This can be done by enabling the “Enable plug-ins only on demand” box in preferences -> Advanced.
Video about the Opera Extentions