Microsoft’s belated disclosure of the space requirements for its innovative new Project Natal interface have struck many as being physically impractical for all but the large living room, with the controller demanding a “clear” space 4m (13 feet) deep.
The device (an Xbox 360 peripheral which uses sensors to interpret bodily movement) is said to require an area significantly larger than most other gaming devices, and more pressingly, larger than many homes or gaming areas can feasibly provide:

To be precise, you’ll want to clear an area extending at least 4 meters (a little more than 13 feet) away from the television.
That’s the back edge of the space to be taken into account by the Natal sensors.
In terms of width and height, the field of vision naturally expands as it moves from the Natal device to that back edge, ending up a little more than 4 meters wide and 2.7 meters high (about 8 feet, 10 inches).

Japanese gamers immediately noticed that this is larger than the size of all but the biggest Japanese rooms – as pictured in the below diagram, previously published by Microsoft during one of its more brutally frank moments:



Possibly this is a significant miscalculation on Microsoft’s part – a “clear area” 4m deep might be a reasonable enough expectation for an American living room centred on a large TV, but in urban dwellings throughout much of Asia and Europe such spaciousness cannot be taken for granted, and even if it could the hassle of clearing away intervening furniture each gaming session might be unappealing.
The 4m space requirement also rules out a significant number of more cramped bedroom and single room dwelling settings. Needless to say, a close-in “PC gamer” style setup with chair, desk and monitor/TV is completely out of the question.
It is not clear how well the unit will function in more confined areas, but it seems likely degraded operation will be possible to an extent. On the other hand, there are clear minimum and maximum range limits with Natal’s sensors which are unlikely to offer much leeway.
More pointedly for gamers (especially slothful ones), Microsoft’s gaming future apparently also involves a great deal of standing up.