Time to clear up the many wrong statements that people are making in this thread. I am the person who made the first powered PCIe extender and who documented why this is necessary: http://blog.zorinaq.com/?e=44

Firstly, the current drawn through the PCIe slot vary a lot depending on the card. Dual-GPU cards usually draw more than single-GPU ones (contrary to what someone said). Here are some of my own measurements with a clamp meter around the 12V lines of a PCIe extender, while Bitcoin mining:

HD 6990: 4.2 A
HD 5970: 4.1 A
HD 5870: 3.2 A
HD 6950: 2.5 A
HD 7970: 0.9 A

So for example the 7970 (and probably most other 7xxx series cards, but I have not tested them) draws so little power that they pretty much don't need powered extenders.

Also, eroxors, most of your cards are pretty low-end/mid-end. They likely all draw less than 3 Amp or so because your most power-consuming one seems to be the HD 5870 (3.2 A through the slot). Even if you had 4 of these cards, that's only 12.8 Amp total, so only 6.4 Amp per 12V wire of your 24-pin ATX adapter.

But most importantly, whether the 24-pin ATX connector overheats or not depends a lot on whether the Molex Mini-Fit Jr. pins in the PSU 24-pin plug have a single or double spring. You can tell by removing the pin from the plastic housing and seeing if it has one or two pairs of "dots" at the end. This one has two: http://www.alliedelec.com/images/products/Small/70090646.jpg The single spring pins (typically used by inexpensive PSUs) have a higher resistance and are more prone to causing the connector to burn out over time.

For example, in my farm of 4x5970 and 3x6990 machines from the old days, I noticed that upgrading from single-spring pins to double-spring pins pretty much made powered extenders unnecessary.

Finally, eroxors, you are right that the memory subsystem of Radeon cards (at least the 5xxx I tested years ago) is powered through the slot, not through the 6-pin or 8-pin power extenders. So Litecoin miners need powered extenders more than Bitcoin miners (at least for 5xxx and 6xxx cards, again the 7xxx series seems to draw so little from the slot, that powered extenders may not be necessary).

Solar is a lot like Satellite TV. When DIRECTV first came out, it was the cool, high-end thing to have. "Get rid of cable" was part of the pitch, but it was no cheaper, and was about $1000.00 just for installation (plus the equipment, which was quite expensive at first). People got it cause they wanted it, not really because of any savings. But then, it started getting cheaper. Eventually, it became a commodity that they install for free, and basically give away the equipment.

Solar energy, to me, is in that early phase. There are a bunch of companies that will install systems, but it is pretty new still, and they can charge a premium. Plus, the equipment is still pretty expensive too. I just had an estimate done for a Solar Hot Water system--JUST the hot water system, and it was 13k. I laughed. But I know that in the not to distant future, there will be huge breakthroughs in the panels, and eventually there will be a DIY Solar Home Conversion kit at Home Depot.

Density my friend, density. When you take into account the platform costs [storage space, mobo, psu, cpu ram], costs will be similar.

7950s, hands down.

1x cables are perfectly fine, you just have to cut off the plastic at the back end. A 16x > 1x cable is nothing else than 1x cable with a 16 connector rather than 1x one of the female side, no extra lanes or anything is actually connected. Like someone else said tho, you will probably need to short the detection pins as well.

the partition could be on a USB memory stick so you could remove it and lock it in a fire proof safe

even if you got the wallet.dat file you need to decrypt it.

people get hacked by downloading another program (like mining software) that key logs their password.