Update: We managed to get in touch with both Wizards and Microsoft PR, who acknowledged that the launch of the DLC did give users a few problems. However, the "DLC is now running smoothly," so happy downloading! You can find the original post below.
Original post: It would seem the recent injection of fresh cards into Magic: The Gathering - Duels of the Planeswalker has had an unintended effect for some players, with the new DLC apparently crashing the game and displaying only a black screen. Users on both the GameFAQs and Wizards of the Coast forums have reported the same issues.
Downloading the Title Update gave us some hiccups -- specifically, we were booted back to the dashboard after downloading it and then were forced to download the entire Magic: The Gathering - Duel of the Planeswalkers game again. But the actual DLC pack itself didn't give us any problems. We even played a game online and tried restarting the title multiple times to repeat the effect to no avail.
Eric Sorensen from Wizards of the Coast's community team is aware of the issue, and WOTC is working with Microsoft to resolve it. We'll let you know when we're all in the clear.
Source - Wizards of the Coast forums
Source - GameFAQs forums