It all depends on what percentage of a layer height your hot end will raise before starting printing. That's a setting of your gcode production software (Slic3r or Skeinforge).
I make the hotend tip just touch the bed (but not push onto it) and have that setting at 0.66 so that the first layer is partially squashed onto the bed.
Some other people leave a paper sheet thickness between the hotend and bed, some says it's not good to squash your first layer (and so raise a full layer height on print start) because it change the object final height, etc...
Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.
