Says Sony: "This maintenance will last roughly 13 hours. During much of this time, users won't be able to access the PlayStation Store, PlayStation Home, Account Management or play online. PSN enabled websites will not be able to service users, including [the PlayStation Blog]."
The maintenance will be to optimize and clean up processes and Sony confirmed nothing is "broken."
When asked for more information on the downtime, Matthew Harper, the Senior Manager of PlayStation Digital Platforms noted "Part of my job is to make sure that the lines of communication are open between our users and PlayStation. While I don't have more details to share at this time regarding the downtime, I will certainly work to include more info in future posts."