50Hz is the standard in the UK, and all PAL and SECAM regions, but it's 60 in the US.
UK Xbox One owners hoping to use the console's TV features are having significant problems. The screen judders so badly that many users call it unwatchable, and it seems the reason for this is that the Xbox is set to a US standard of 60Hz, while UK is a PAL region. PAL and SECAM regions are set to 50Hz standard. Pushing a 50Hz signal through a 60Hz machine just isn't fun; frames start to drop, and the picture is significantly degraded.
This suggests that, of the 13 launch countries, Xbox TV functions may not work very well in Australia and New Zealand, among others. These may be less affected than the UK; Australia and New Zealand are switching from PAL standard to DVB-T, and most European nations have switched to DVB-T standard. At time of writing it's not confirmed whether, or how badly, those regions are affected by the problem.
According to CVG, it's possible to fool the Xbox One into outputting video at 50 rather than 60, which solves the TV problem. However it causes a game problem, because many of the Xbox One's titles are set to 60Hz.
Digital Foundry's Richard Leadbetter has told Eurogamer that there's no easy solution. "The kind of frame-rate upscaling required to eliminate the judder at 60Hz would probably compromise image quality." While setting the machine to 50Hz during TV and switching it back to 60 for gaming was doable, "this wouldn't be quite as seamless an experience as Microsoft originally envisaged," says Leadbetter.
Microsoft has said that it is aware of the issue, but had no comment, or solutions, yet.