Everyone has seen or heard about using the +5v on the molex connector as a fan's ground to effectively run your 12v fans at only 7v in order to reduce fan noise. And there have been mods where you can have a rheostat to vary the fan speed by using voltages in between 7v and 12v.
Well whoop-de doo. Since when has it been in the mentality of a performance freak to run any hardware BELOW spec?
Well here is a really neat and easy way to make your fans run faster than ever - just up the voltage!

Bullshit. Take a look at the atx connector that is powering your entire motherboard. There are all sorts of voltages on it. Here's a photo from a motherboard manual to show you them.

Now you see where I have put a red arrow? Thats the -5v line coming from your power supply. If you connect the positive (red) wire of a fan to the normal +12v on your molex connectors, and stick the black wire onto -5v on the atx connector you get : 12 - -5 = 17volts running through the fan!

Now here are some pictures of it all in action, and I apologize for the quality it was almost impossible for me to take closeup pictures in such a crowded case, in pitch darkness (I can't afford lightbulbs).

Here is your average 12v fan. Red wire. Black wire. Take the black wire and the story ends. You wake in your bed
and you believe whatever you want to believe. Take the red wire and you stay in Wonderland and I show you how
deep the rabbit-hole goes...

17 Volts: Stick the red wire in the +12v (yellow) of the molex. See where I stuck the black wire? That's the -5v on the atx connector. Mine was a white wire, but this could vary between power supplies. Be sure to check your mobo manual for the orientation of things, so you know what wire does what. Now I just jammed the black wire down the inside of the connector and it worked - but this isn't a good permenant solution. A better one would be to splice the wire (with power supply off you moron) and make some kind of a -5v hub wire for all your fans to connect to.

24 Volts: Leave the red wire on +12v, and move/splice the black wire to the -12v line according to the atx connector diagram.

Results and comments:
This is probably the only truly serious mod on Afrotech so far, so sorry if its boring you! I looked around on the net trying to see if anyone has realised this trick yet, but I only found one mention of it in a Hardocp guide that seems to be long forgotten. Anyways, yes this mod works. 17v gives you noticeably more air flow, and at 24v the fans scream like 7krpm deltas. I tried it with an 80mm, 120mm, and one bigass mutha of a fan that was probably capable of being a speedboat propellor. All worked, and were capable of taking 24v for several hours. The drawbacks are that I am sure your fans life will decrease, and I have no idea if they can run at 24v for a useful period of time. Things also get damn noisy.
I would recommend you give 17v a shot, especially if you have good quality fans. If you have a spare fan lying around, juice it with 24v and see how many days/weeks/months it lasts for, then maybe you can try it with more of your fans if you think its safe.
Just don't be a moron and write to me saying "I ran my cpu's fan at 24v and last week it died overnight and my computer caught fire and it set my house on fire and now my parents are DEAD!!"