Don't let their brown-ish color fool you. Those leaves can contain 50 to 80% of the nutrients that a tree pulls out of the soil and air during the past year and often contain valuable micro-nutrients according to a Rutgers University study.
There are three ways you can utilize leaves in your landscape.
Mowing leaves is a great way to shred the leaves into smaller sizes, making it easier to just drop them right back on the lawn. Be sure to rake the bits into the grass so that they don't smother the blades completely, much the same way that you apply compost.
Fall leaves can also be utilized as mulch. Mulch will help protect your landscape from winter freezes and helps retain soil moisture. Shredding the leaves ahead of time with your lawnmower will prevent them from blowing away and speed up the natural processes that convert mulch to compost. Another great place to add leaf mulch is in between your vegetable beds where they become walkways during the (hopefully) wet days to come.
Incorporate composting into your fall maintenance strategy so that no leaf escapes your property. In general, you can use three times as many leaves as materials like lawn clippings, kitchen scraps or coffee grounds. A well-mixed pile that is turned once a week can yield usable compost in one to six months. An additional benefit to hoarding leaves is that you can use them to build layers in your compost or cover scraps as they are added to the pile.
Keeping leaves out of landfills and waterways helps the environment and your garden by recycling nutrients close to where they were taken out of the soil.
You can find more information on composting leaves at Earth-Kind Landscaping.