Finished building printer & itching to print. One question remains regarding Z-Axis end-stop...

I just finished building a prusa i3. The build went fine, everything is working as it should, all leveled, etc.. So, I was testing my z-axis end stop and quickly realized that I had a faulty switch. The manufacture is sending me a replacement, but, it will take a week or so to get it here. In the interim, I purchased a switch from Radio Shack that was almost identical to the original, so I could test the printer out and familiarize myself with printing... I tested the switch and it is working correctly.

But, I need help understanding where exactly the switch needs to be placed. I understand where it /should/ go, but, can't figure out if the switch is suppose to be tripped once the nozzle touches the print bed? Can anyone explain where the nozzle should be relative to the z-axis limit switch being tripped?

when homed on the z axis the tip should be about .1mm from the bed (thickness of a standard sheet of paper)

Just to add to that, if you built an i3, you have a bed held in place with either 3 or 4 points. I'll assume 4, one in each corner, although I prefer 3. You need to set the bed so it is the thickness of a sheet of paper at all the points where the bed is connected to the chassis. The way I do it (borrowed from the wiki) is to lower the nozzle onto the bed with a sheet of paper between it and the bed. I pull at the paper and if it pulls out with a bit of resistance I go with that.

It's important to do it at all the points though, and once you've done all four, DO THEM AGAIN, as changing one changes the alignment of the plate. You have to repeat the process until they are all equal.