Patch 4.0.1 Release Date Confirmed!

Patch 4.0.1 Release Date Confirmed!+ Patch notes

Quote from Bashiok: (source)

Extended maintenance will begin tonight at midnight, Tuesday, October 12 for the release of patch 4.0.1. Maintenance will begin at 12:01 AM PDT and conclude at approximately 12:01 PM PDT. During this time all realms and many web services will be unavailable. 

Due to the size of the patch we highly recommend you enable your background downloader. If you need assistance doing so please visithttp://us.blizzard.com/support/article.xml?locale=en_US&articleId=35274

Changes for the patch can be found from here: 4.0.1 Patch Notes