At $519 US you just need to ask yourself one question. Do you want the fastest single GPU card available? If the answer to that is "Yes", then this is the card for you. The GTX 580 is fast; when overclocked it's faster again. Overclocked even more due to the extra abilities you get from the "Lightning" series and you've just got a card that's Lightning fast. Excuse the lame pun!
Something that's so important to know about the Lightning series is while MSI put a huge amount of effort into making them the best cards for people who are doing extreme overclocking via LN2, they're a fantastic card for people who are just interested in overclocking on the cooler.
The ability to have more voltage options means that clocks can go higher than other cards, and in the software MSI allow only options that are safe on the solution they provide. Combined with Afterburner you can have a real blast with the Lightning series on the provided coolers. The fact they're also a lot more efficient than the reference coolers means that the headroom for overclocking is also increased.
The HD 6970 Lightning is a better value card; it's cheaper and offers great performance. The GTX 580 Lightning is a faster card, though; it costs more, but offers more performance. For people who demand speed, this is the card to get and while dual GPU offerings like the GTX 590 and HD 6990 are great, if you've got the room and the money, SLI or CrossFire offerings of these Lightning cards are going to be even better.
Don't be scared off by the ability to measure voltage from the card or the "LN2" BIOS, because as we mentioned, while this is a fantastic card for those extreme overclockers, the engineering that goes into this card, the out of the box cooling solution and the ability to adjust multiple voltages also makes this a fantastic card for people who will use the stock cooler.