I want to get a graphics card after Kepler and Tahiti come out but I have a nagging worry in the back of my mind that if I get a higher end card like a 680 or 7980 (or whatever) that my CPU will get bottle-necked. How much GPU power does it take to bottleneck an i5 2300?
The cards have not yet released, so we do not know what bottleneck will be present. Based on the current high-end cards (technically it's 7970, not 7980), there should not be a major, if not any, bottleneck. Even with a GTX 580 or HD 6970, you'll be fine.