Fallout: New Vegas is a notoriously buggy game, and fans have patiently waited six months for critical patches. Now that one is on the table for Xbox 360, Bethesda is warning people against downloading it, due to save files being corrupted. Bethesda announced via Twitter that it is aware of the issue and that, "We're working with Microsoft on this and should have more information soon."
Most frustrating is that there has been no official word from Bethesda, no press release, no email, nor any communication outside of that single Tweet from yesterday that might warn fans about the issue, and save face for Bethesda in the process.
For now, the best thing Xbox 360 owners can do is decline the update and wait for future announcements.