A metal pin or paper clip is heavier than water, but because of the surface tension the water is able to hold up the metal.
Surface tension is not the force that keeps boats floating. If you want to know why a boat floats look here: Why do boats float?

Capillary Action

Surface tension is related to the cohesive properties of water. Capillary action however, is related to the adhesive properties of water. You can see capillary action 'in action' by placing a straw into a glass of water. The water 'climbs' up the straw. What is happening is that the water molecules are attracted to the straw molecules. When one water molecule moves closer to a the straw molecules the other water molecules (which are cohesively attracted to that water molecule) also move up into the straw. Capillary action is limited by gravity and the size of the straw. The thinner the straw or tube the higher up capillary action will pull the water (Can you make up an experiment to test this?).
Plants take advantage of capillary action to pull water from the into themselves. From the roots water is drawn through the plant by another force, transpiration. Click here for more information about transpiration.