Microsoft's scheduled maintenance of Xbox Live came to a close this morning, but not without a few kinks. Kotaku reports several post-maintenance issues with the Xbox Live Marketplace, including errors when downloading certain pieces of content, issues with redeeming Ghostbusters preorder bonuses, and even a few games that are now missing entirely from the service.
The official XNA Community Twitter states, "We know there are a few issues and top agents have been deployed to resolve them. Thanks for understanding!", while Microsoft's Xbox Live support page offers a more formal apology:

"Users may experience difficulties when attempting to use Marketplace and/or making purchases. We are aware of the problem and working to resolve the technical issues. We apologize for any inconvenience this may cause and thank you for your patience."
Hopefully they'll be able to work this stuff out sooner rather than later. We'll keep you updated as Microsoft attempts to resolve these problems.