Any thoughts/ideas how they did this?
http://www.apple.com/ipodnano/ads/

That is impressive, all right! Here is how I would do it:

Motion capture the people using chroma key.
Create the lights in a 3D application like Maya using the tracking data from the previous part.
Composite the two, paying attention to the z-layer to make sure the light gets obscured by the subject when it passes behind him.

I think the lighting was done at the shooting stage too; it would certainly be easier than doing it in post-production.

I haven't found anything spefic on this yet, but here's my guess...

Film with three cameras, the one for the ad, plus two more at off angles to capture the 3d motion of the iPod.
Then the tracking data could be used to create the ribbon of light in 3D and that could be matchmoved into place based on the view of the main camera.

trapcode particular

Andrew Kramer (http://forums.creativecow.net/articles/kramer_andrew/nano/index.htm) has a great tutorial on how to do the streaking with After Effects.

trapcode particular

could you explain that please, how would that work? thanks.

Trapcode Particular (click here) (http://trapcode.com/products_particular.html)

i understand now. thanks.

A buddy of mine sent me this link a while back that provides a pretty good solution for how to do this in After Effects!

http://ayrshire.creativecow.net/articles/kramer_andrew/nano/index.htm

I doubt it's how they actually do it for the commercials, and it does require a third party plugin for AE, but the result is impressive to say the least.

Hope it helps!