I consider 0.6 BTC/share to be overpriced, therefore a risky investment. But that is just my opinion. I tend to be conservative. Other investors might think differently.
How can 0.6 BTC per share be overpriced? In no way thats true. I got 0.02135376 BTC per share in each of the last 2 weeks. 52 weeks with this are 2.22BTC.
Your math completely fails to take into account how quickly difficulty is going to rise.
Look, even friedcat estimates that ASICMINER will average only 10% of the global hashrate over the year. It means each share will bring: 25 (coins/block) * 6 (block/hour) * 730 (hours/month) * 9 (months) * 10% / 400k (shares) =
merely 0.25 BTC of revenue between now and Dec 2013 (1/10th of your "2.22 BTC" estimate!)
Plus the 0.25 BTC of revenue per share assumes 100% of the mining revenues are going to be distributed to shareholders. We know this is not going to be the case given friedcat's plans (he will reduce the dividend).
And in 2014, all bets are off. ASICMINER's efficiency (130nm chip) is relatively bad compared to other ASICs (55-65nm). They are not hosted in a country with low electricity prices. I can't see how they will remain profitable in 2014. Plus I think 10% of the global hashrate is itself an optimistic estimation for 2013.
This is why I think 0.6 BTC is overpriced for a share that definitely will not return more than 0.25, maybe 0.3 or 0.4 BTC if being overly optimistic.
The only possible justification for a price of 0.6 BTC/share is
if you assume that ASICMINER is going to plan to build a more efficient chip, and
if they are going to succeed, and
if they are going to deploy and ramp it up as fast as (or faster than) the competion. But at this point it would be a very speculative gamble. There are too many "ifs" for me.