Mining stocks and maybe the bonds issued by them seem to be the only thing currently besides gambling that seem to be stable enough to survive in a bitcoin only economy.
How are mining investments more stable in the face of an unknown number of ASICs being released at an unpredictable pace?
Mining is about the most predictable form of BTC investment around - it'll lose money (all the time it's profitable more people will start mining until it ceases to be profitable - meaning a loss for investors unless you find one of the rare investments where operator's pay comes from profit not turnover when you'll break even or make a tiny profit). Only the very first wave of ASICs or those investments with some significant edge (manufacturing ASICs, very cheap power etc) will ever make any noticeable profit for investors - the rest just earn cash for operators whilst losing investment capital.
The general problem with BTC investments is that with BTC being deflationary by design very few fiat-denominated investments stand any chance of producing (BTC-denominated) profit - they can make fiat-denominated profit but will still be likely to end up worse than idle BTC would. That will tend to balance out long-term -as deflation will be curbed by a lack of utility (reducing demand), leading to a state of equilibrium. But we're some way off that (like a few years).
Investments like this are sort of good for the community/BTC as a whole. Although the odds are very heavily in favour of investors making a loss (that's by no means uniquie to BTC - most startups fail period), at least by doing so they're spreading the word about BTC. It's unfortunate (when it comes to investment) that BTC is deflationary - as even when I see half-decent investment opportunities I KNOW that statistically I'm better off with BTC in my wallet than investing (if BTC succeeds the idle BTC will appreciate in value more than any traditional business - especially considering a 90% failure rate, if BTC fails then either way I've lost - so why invest?).
Note that I see a strong distinction between investing (buying shares to make a profit from the dividends or growth of the company) and trading (buying to sell higher and make a profit from the market). Something like this I'll happily trade (buy the early-bird shares and flip them below 2nd batch price) but without assets backing the shares there's no way I'd personally invest. There's definitely far worse investments around though (e.g. the two blatant scams currently listed on Bitfunder).