What I really worry about, is that new hardware will continue to come out frequently enough that people end up on a cycle of investing in hardware that basically never pays itself off as slightly newer hardware and higher diffs keep coming out. Sure at some stage the limits of technology will be reached, but given the best tech at the moment is going to be 65nm ASICs when CPUs are 28nm devices, I can see the cycle going on for some time, and then even if btc mining ASICs end up in line with CPU manufacturers, they still continue to evolve over time. Dramatic profits from ASICs will likely only last a couple of weeks at most for a lucky few. The rest of you who paid for devices that don't even exist yet will not be making any magical profit no matter how big the hashrate appears. Your proportion of the total bitcoin hashrate will remain pitiful.
Sigh...
There's definitely some merit to this, but remember, the exact same thing happens with Video Cards, every 9-12 months the new GPU cards hit the market and are more efficient at mining. Of course video cards are much less expensive than the current round of ASIC's and can be resold.
Not *that* much more expensive. A 7990 will run you real close to what a 74GH/s bASIC will.