Mike, I think you can most anything you'd need to with CS6, but not so much with earlier versions. With CS6 you can change the opacity, or copy all the selected layers for instance. I don't think you could change the opacity of licked layers with CS5
BUT and it's a big but..
If you right click those linked layers and make them a Smart Object, then you can do lots of stuff with it, and edit individual layers later if you should so need to.
That link doesn't work for me.
I think it's missing .html -- http://help.adobe.com/en_US/photoshop/cs/using/WSfd1234e1c4b69f30ea53e 41001031ab64-78d2a.html
Linking layers is similar grouping layers in a sense, but a bit different as well.
So you can have multiple layers retain their relationship to each other as you move them around, or transform them and they will transform together.
Unlink them and they will act separately
One difference of linked layers vs grouped layers is that you can move a linked layer up and down your layers panel, in and out of groups, and still maintain it's link to the other layers which may reside in a group. So that if you select that layer and move it on the canvas, it will still move with the layer it's linked to even though it's outside the group.
You can link multiple groups together as well.
So what 'retain their relationship' mean? Do they retain stacking order? What properties are effected by linking? Are there any visual indications of which layers are linked?
Stuff like that
I was meaning they retain their positional relationship to each other. In otherwords they move at the same time.
Here is a screenshot of what linked layers look like. If you have a layer targeted in the layers panel and it is linked, it will indicate which layer it is linked to by a chain-link icon on the right side of the layer.