Apple sent out the following emails to developers this afternoon:
iTunes Match Update
As we prepare for the launch of iTunes Match, we will be deleting all current iCloud libraries on Saturday, November 12th at 10 AM PST.
Please turn off iTunes Match on all of your computers and iOS devices. On your computer, choose Store > Turn off iTunes Match. On your iOS device, tap Settings > Music, then turn off iTunes Match. On your Apple TV, please choose Music > Turn off iTunes Match.
The songs on your computer should not be affected. As always, please backup regularly and do not delete the music you add to iCloud from your computer.
Apple Developer Program Support
Though Apple doesn't overtly say that the iTunes Match launch is impending, the email differs from others Apple has sent to developers in the past by mentioning a specific time for the deletion of developer's iCloud libraries and also states that it is "[preparing] for the launch of iTunes Match."
On November 1st, Apple officially missed the release date for iTunes Match. They had previously said the service would be available "by the end of October." When iTunes Match does officially launch, it will cost users US$24.99 per year. The service will scan your iTunes library for titles, match them with copies in the cloud, and then allow you to replace whatever copy you may currently have in your iTunes library with a non-DRM, high-quality 256-Kbps AAC copy.