Ask Mr. Smarty Plants

From About.com: Forestry Reconsider Planting Leyland Cypress in Your Yard, we extracted the following information:

"This rapidly-growing tree quickly outgrows its space in a typical yard unless properly and regularly trimmed. Leyland cypress only lives for twenty to twenty-five years. I've found that trees left to grow large may have limited root support and are the first to blow down during high winds. You should consider the work needed to maintain a Leyland cypress before planting."

Having said that, and admitting that the Leyland Cypress is a non-native hybrid and has some disadvantages, we don't know that we would cut down and take away already established trees, especially if they are where you think they will do the job you need done. It does need full sun, and requires a great deal of maintenance to keep it in check. If you don't have full sun for the trees to grow in nor the gardening energy to keep it pruned and under control, then you had probably better replace them with something else.

In terms of using bamboo, please don't do that. It is non-native, fast growing and predatory. It will take over your garden, your neighbors' gardens and your life if you are not careful. See this article from eHow on How to Get Rid of Bamboo. Our suggestion for getting rid of it is-don't plant it!

We are trying to visualize your situation; you say your yard has lots of trees and is very shady in warm weather, giving you the privacy from near neighbors that you desire. So the problem would seem to be, gaining that privacy in winter when the other trees are bare. You don't really need a hedge, and you already have 8 ft. of fence, so you need to survey exactly where the "holes" in the privacy are in the winter. A vigorous shrub or small tree, trimmed up as it grows into tree shape, would surmount the fence with a green crown, without crowding the other trees lower. This doesn't happen overnight, however, and in the meantime, that shrub/tree is going to need at least some sunshine and room to grow. If, for instance, you position such a plant closer to windows in your house, that will more readily close off your view of your neighbor's windows, and vice versa. We will look in our Native Plant Database for some trees or shrubs native to Georgia that we think might work for you. Follow each plant link to the page on that plant in our Native Plant Database to learn other characteristics and care.

Evergreen Shrubs or Small Trees for Cumming GA:

Ilex opaca (American holly) and Ilex vomitoria (yaupon) - both of these shrubs/small trees can grow in sun, part shade or shade, are evergreen and can make attractive dense-canopied trees

Magnolia virginiana (sweetbay) - part shade, relatively fast-growing, is considered semi-evergreen but would probably be evergreen in Zone 7, north central Georgia

Prunus caroliniana (Carolina laurelcherry) sun or part shade, 15 to 20 ft., seeds, twigs and leaves all poisonous so not appropriate for garden accessible by children or pets

From our Native Plant Image Gallery:

Ilex opaca

Ilex vomitoria

Magnolia virginiana

Prunus caroliniana