You could cart that mower clear across town to a service shop, wait a day, go back, and fork over $15 for getting its dull blade sharpened. Or you could do it yourself in less than 30 minutes for free. Safety first: Pull the spark plug to prevent an accidental start-up. Next, tilt the mower, following the manufacturer's instructions, and wedge a scrap of 2x4 against the blade so that it won't turn as you unbolt it. Mark the blade with an X to indicate its face for reinstallation. Clamp the blade in a vise, and make long passes along the beveled cutting edge with a 12-inch mill bastard file (yup, that's what it's called). The stroke begins with the top of the file near the center of the blade and ends when you feather the bottom of the file off the blade tip. Once the edge is shiny and ding-free, check the balance by centering the blade on a nail driven into a piece of wood. Make extra passes with the file if you need to level it. Bolt the blade back onto the mower and you're ready to sling grass again.