Thanks for the info Bitcoinorama and all the other folks that contributed. I think I've made up my mind about KnC and asic purchasing in general.
The way I see it. The arrival of asics in rapid and large scale as Knc and several others propose will kill profitability in the short to medium term. People who have invested thousand of dollars in asics will try to dump their bitcoin as soon as they mine it to pay for their investments before the dif goes through the roof. This will create a buyers market and the price of btc will plummet.
The smart players and long term investors will hoard and bottom feed but they will be the few. Many many more will sell as long as its still profitable for fear of losses. Unfortunately human nature being what it is a lot of people have jumped in feet first thinking this would be an endless source of easy money, probably going into debt to fund it. They will be the first to panic and flood the market with cheap coin. This will probably start a snowball effect that will collapse the market for months until things level out. The proverbial "fire sale"
And when the dust settles the time for small miners will be gone. Unless you are willing to constantly upgrade and treat this as a business you will eventually have a nice warm metal brick sitting in your garage. Bitcoin will be dominated by those with deep pockets and ebay will be flooded with cheap asics.
This might sound alarmist but this has a similar feel to the dotcom and housing bubbles that many people lost their shirts in. People saw a rising market and jumped in without looking at the fundamentals betting more than they could afford on the promise of easy cash. Not that long ago btc was at $260 probably for the same reason. Fools rushing in.
Personally, I'll just keep my renderfarm (12gh) chugging away at ltc and leave asics to the gamblers, for now.
ASIC hashrate will be limited by the same factor that limited GPU nad FPGA hashrate: money. The same people are converting their farms to ASICs, some new ones are investing in new farms (some poor souls jut bought their FPGAs/GPUS and might be out of the ASIC race), but overall, the money spent on ASICs will be roughly the same as the money spent on older technologies.
I expect the sharp raise in difficulty to top off in the 10-20x range, then resume the 10% increase, probably followed by a small dip (as seen in the GPU and FPGA ramp ups).
Small time miners will still be able to use GPUs if their electricity is cheap or they will be able to buy cheap 5GH/s miners at around 300 USD. The equipment will be less versatile, so it will indeed deter casual new entrants, but I don't think it will deter the more serious ones.
Also, I don't think the fire sale will happen. We might see an increase in BTC being converted by new entrants, but the bulk is still in the hands of the current miners who are just converting to ASICs to keep their revenue level, so I wouldn't worry too much. The current price is probably still inflated, so it might indeed crash, but I don't think it will be because of miners dumping their coins (besides, if it becomes unprofitable to mine, they will shutdown the equipment and the others will profit from a lower difficulty and a new cycle starts).