When we design a system here, we usually try to start the first run of elements at the toekick of a bathroom vanity because of the potential for this problem (which is why we can be sticklers about the measurements people send in for us to quote off of).  The cool floor under a vanity can wick heat away more than people think.

As for installing under laminate or hardwood, you do not need more power to make those floors warm, but you may need to better insulate below the elements (always important, even under tile).

And if you decide on hardwood, you'll only have to run the elements perpindicular to the flooring and nail away, just don't hit a bus braid (the wire that runs down either side of the element).

for more information, scroll down and click on the STEP Handbook link in the Popular column.