The Congressional Research Service report, The Economic Effects of Capital Gains Taxation (R40411), is available on OpenCRS. Here is part of the summary:

Some argue that reducing capital gains tax rates will increase tax revenues by dramatically increasing capital gains realizations. While the effect of changes in the capital gains tax rate continue to be debated and researched, the bulk of the evidence suggests that reducing the capital gains tax rate reduces tax revenues. …

Capital gains tax reductions are often proposed as a policy that will increase saving and investment, provide a short-term economic stimulus, and boost long-term economic growth. Capital gains tax rate reductions appear to decrease public saving and may have little or no effect on private saving. Consequently, many analysts note that capital gains tax reductions likely have a negative overall impact on national saving. Furthermore, capital gains tax rate reductions, they observe, are unlikely to have much effect on the long-term level of output or the path to the longrun level of output (i.e., economic growth). A tax reduction on capital gains would mostly benefit very high income taxpayers who are likely to save most of any tax reduction. A temporary capital gains tax reduction possibly could have a negative impact on short-term economic growth.

(Hat Tip: Jon Forman.)