Below are some quick quotes from various articles which I hope will convince you of the need to seal up all those tiny holes, cracks, & crevices around your house.

My Thermal Inspection can show you exactly where they are!

1. Whether it's summer or winter, energy moves through the walls, roof and cracks of your home. Either cool air conditioned air is lost to the outside during the summer or cold winter air is finding its way into your home during the winter.

Where does a home lose heat energy? Well you can generally categorize it into five areas:

• Ceilings
• Walls
• Floors and Below Grade Space
• Windows and Doors
• Infiltration (air leakage)

No, these are not all the same in terms of their contribution to heat loss. Heat is lost to infiltration and air loss by over 3 times the amount it is lost due to ceilings. These categories generally stack up this way in terms of % heat loss in a home:

• Infiltration / Air Leakage: 35%
• Windows and Doors: 18%-20%
• Floors and Below Grade Space: 15%-18%
• Walls: 12%-14%
• Ceilings: 10%

If you were to get ready for winter your inclination would be to buy insulation wouldn't it? Well it's not the best investment (although always a good thing). Reducing your air leaks around plumbing vents, wall electrical outlets and switches, recessed lights exposed to the attic, attic stairs, vertical plumbing stacks open in the basement and other culprits all allow heated air to be drawn from your home and escape out the roof or other openings.

Focus on buttoning up your home to air infiltration and leakage first including windows and doors, then focus on investing on insulation. Also, consider insulating the attic first.  — About.com: home repairs

2. "A typical household spends about $2,000 a year on energy bills and contributes twice the amount of greenhouse gases to the environment as an average car."  — http://www.energystar.gov/index

3. "The bulk of energy loss is caused by dozens of small holes and cracks around your home that allow air leakage. It seems unbelievable, but if you added up all the holes in an average home, you'd have a giant 5' hole in the wall. Ouch! That's the same as keeping your front door open all winter.

Of a home's total air leakage, approximately one-fifth occurs in the basement: 1 percent passes out through basement floors and 20 percent through basement walls. Walls and ceilings account for another 22 percent of air leakage: 17 percent and 5 percent, respectively. All those wires, pipes and ducts running through the walls and ceiling let cold air in and warm air out.

The biggest culprits are all those big holes in the building, also known as "doors" and "windows." Doors account for 3 percent loss, windows account for 16 percent, and cracks in walls, windows, and doors, account for a whopping 38 percent.

The easiest and least expensive fix is to purchase a can of expanding insulating foam found at home centers and discount stores. Then look around your house for holes, cracks, and gaps and fill them."
 — asktooltalk.com

4. Adding more and more R-Value is like adding insulation to a thermal coffee mug. You can keep making the mug thicker and thicker with more and more insulation (R-value), but if the lid is left off, the contents will still get cold. That's the impact of air leakage!  — www.insulationsmart.com