[changz (OP)]

Suppose that I have a REALLY REALLY strong magnet, and a nail REALLY REALLY far away. When the magnet attract the nail, would there be a time lag??

[lightarrow]

Suppose that I have a REALLY REALLY strong magnet, and a nail REALLY REALLY far away. When the magnet attract the nail, would there be a time lag??

Of course. Magnetic force travels with the speed of light (at best).

[lyner]

Suppose that I have a REALLY REALLY strong magnet, and a nail REALLY REALLY far away. When the magnet attract the nail, would there be a time lag??

We're back to the same problem as when considering  'suddenly taking the Sun away'. Things don't suddenly appear or disappear; there has to be some energy expended in order to cause this. To make a "strong magnet" you need to build up the field and that involves a change of electromagnetic energy (however you choose to do it). That change will cause a magnetic pulse which will propagate through Space at c.

[changz (OP)]

so do you mean that magnetic field are particles? Then are there barriers? Or... can we distort them?

[syhprum]

The attraction of magnets is a property of the electromagnetic field which is mediated by Photons which of course travel at the speed of light.
When you attract your nail there is an additional delay as the magnetic domains in the nail orientate.

[lyner]

I suppose it would be churlish to ask about the actual energy content of these photons and why the process can't be discussed in terms of a continuum. Photons are vital in some discuusion but, here? EM waves travel at c, so why not just talk about waves?
The field which the magnet sets up affects conductors of electric current (involving more fields). The 'distortions' result in forces - hence Magnetism is observed.