ZOTAC's GeForce GTX 580 AMP! Edition does not bring many improvements to the table. The card is a complete implementation of NVIDIA's reference design with higher clocks. Its increased clock speed of 815 MHz, vs. 772 MHz on the reference design, can deliver a small performance improvement in our benchmarks - up around 3%. If you are willing to do some additional overclocking then you can expect a higher clock headroom on the AMP! Edition than on other reference design cards. According to ZOTAC, some special binning is performed at the factory where GPUs are picked that can handle the highest clocks. Compared to other reference designs, which max out at around 830 MHz, the 895 MHz on the AMP! Edition are a good improvement.
Whereas the GTX 480 AMP! Edition used a Zalman cooler, ZOTAC's GTX 580 AMP! comes only with the reference cooler. I talked to ZOTAC about the cooler and they mentioned that they were planning on using a different cooling solution but at the end it didn't work out for what were mostly political reasons beyond ZOTAC's influence.
Overall the GTX 580 AMP! Edition is a solid card but feels a bit too expensive with a $50 price premium over the normal clocked cards.