OK, now I'm starting to feel like Andrew (apepp) with a whole slew of posts, but hey...
Another cool thing you can do with Paste-in-Front is when you want to add something to the contents of a clipping mask, just Copy or Cut your object, then select the contents of the mask but not the mask itself, and Paste in Front, voila your object goes into the mask in front of the other contents.
One thing you'll notice, is that if you Copy, and then go to the next layer and paste in front, sometimes it will paste back on the original layer. If you make sure to deselect the contents of that layer, this will not happen.
One last thing, if you want to take contents of a number of layers from one document and paste them into another, you'll get everything on one layer. To prevent this and essentially paste with the layer structure intact, you can go to the layer flyout menu, and towards the bottom check the option "Paste Remembers Layers". Don't forget to turn the option off again after you're done.
HTH
Bert