I've had my KSO's a month, and they are beginning to hum. (What really started them off was walking through dirty street water in London a few weeks back, and also wearing them in a communal shower in a backpackers hostel, then wearing them wet walking round the city....Yum yum...)
I've read through this entire thread, and while I'm sure Oxi-Clean is really good stuff, and WIN sports wear wash, too, neither of these are readily available in the UK sadly.

So what can we use, this side of the big pond?
I saw that the Oxi-Clean product was a stain remover which also came in a powder, and checked out what was available at my local Tesco. I came away with "Vanish Oxi-action powder with antibacterial action."
This is the kind of stuff - in the hideously pink tubs - costs about £4.50 a tub.
http://www.britsuperstore.com/acatalog/Vanish_Oxi_Action_1Kg.jpgSeeing as others seem to suggest it may be the bacteria in the shoe contributing to the stink, I picked the powder with "antibacterial action - kills 99.9% of germs." I'm not normally a freak for hygiene, but I'm going for smell elimination here, so thought I'd give it a try.
I have just put 4 litres of hot water in a washing up bowl, added 1 scoop of Vanish powder, inserted shoes, and wearing gloves I scrubbed the buggers with a toothbrush, all inside and round the toe pockets, and in between the toes, as advised by others, and also round the inside of the footbed. I only left them to soak for about 15 - 20 mins, as am being cautious. The water went a minging brown....

I then rinsed them out thoroughly in the shower.
They are now hanging in front of a fan drying. Will give you an update on the smell factor tomorrow... or whenever they are properly dry!!!

Additionally I am also going to take the advice of getting some tea tree essential oil, and wiping my feet over with it whenever I wear my KSO's, with any luck that should discourage bacteria buildup, if not the muck!
ETA: I've just had a thought - would antibacterial hand gel (bought for the Swine Flu scare last year...) work on eliminating stinky foot KSO's? I've half a little bottle left, might be worth a try before I buy tea tree stuff...