How long should an auto or manual be left not running?

http://omegaforums.net/threads/1969-seamaster-chrono-value.1656/page-2#post-17924

As a newcomer I've often read that such watches should be kept running otherwise the oil will thicken. Is this incorrect given the market for winders or are they for people who can't be bothered to wind after rest periods?
For vintage motorcycles, that I know more about, it's not good for seals if they don't get lubricated by running the engine regularly (not just ticking over) with frequent oil changes recommended.

The lubricants in a watch are much better now than decades ago. I would run a watch once every two or three months at least but even that might not be necessary. If it's only for collecting purposes and doesn't get worn then don't worry about it.