From what I gather, it's pretty easy to make and homemade/fresh usually tastes better than commercially produced...
HOMEMADE LIMONCELLO
Makes about 2 1/2 quarts.
Note: In Italy, limoncello is generally served after dinner as a digestive, often in chilled glasses. The author of this recipe uses organic lemons and the Microplane grater, a variation on a wood-working tool that is readily available in kitchen stores. Zest is finely grated peel; make sure not to grate the white pith of the lemon, which is bitter. The author uses half cheap vodka and half more expensive for the alcohol, though traditional recipes will call for clear grain alcohol that's 97%. She recommends a full five days for flavoring the vodka with the lemon. She prefers cane sugar, which is less processed white sugar, and is available at natural foods stores.
? 2 lb. lemons
? 1 quart (4 c.) clear grain alcohol such as vodka
? 6 c. purified water
? 2 1/2 c. cane (or granulated) sugar
Directions
With a very fine grater, zest the lemons. Put zest and vodka in a tightly sealed jar or bottle large enough to accommodate at least a quart of liquid.
Place container in a cool, dark and dry place for at least 3 to 5 days. Shake the jar at least twice a day. Zest will turn white when flavoring is done. Strain the zest from the liquid through a fine sieve; discard the zest and set aside the flavored vodka.
Place 6 cups water in a saucepan over low heat and add sugar. Heat, stirring occasionally, until sugar dissolves and syrup is clear.
Cool syrup to room temperature and mix with lemon vodka. Strain the sweetened lemon vodka through several changes of coffee filters and store in tightly sealed bottles in the refrigerator. Chill and enjoy.
*More traditional recipes call for steeping up to 60 days. However 3-5 will produce good results. Also, note that this does have a shelf life - that's the reason that the commercial ones generally don't taste as good.