If the exchange rate is still $12.32/BTC on halving day I'll drop to $0.43/day.
Presuming you are like most other GPU miners and pay a normal electric rate (e.g., $0.15 per kWh) then your electricity for the rig will likely exceed $0.43/day.
But let's say it is break even. You'ld rather pay $12 to your electric company for a month of mining which yields 1 BTC versus sending $12 to an exchange and getting your 1.0 BTC that way?
And if your electric bill comes in higher than the $0.43 per day, then you are paying above market rate to buy -- and you are going through the effort of managing a rig for free.
If it is a hobby, then call it a hobby. But anyone mining GPUs for the purpose of profit should know right now ... in about 60 days the party is over. [Edit: Of course, there are other uses for your GPUs, but mining BTC for-profit is specifically what I'm addressing.]
No - everyone was making statements like this when btc was 5.50 with lower difficulty. halving the block reward is effectively the same as halving the price of btc. People are were still mining at 5.50, and 2.50, and 0.02.
Minor point, pools may need to charge higher fees.
Major point, tech change - ASICs coming out, what if you're lovely BFL SC single is only netting you $120 per month (40x difficulty) - extreme example, but thats the only uncertainty in btc right now, the potential for asic mining to kill the hobbyist aspect by making gpu mining pointless, thus killing demand for btc in general.
Personally, I think we'll see a 10 or 20 times increase in difficulty once asics saturate the market... which probably won't make gpu mining die entirely, if it comes with the price increase expected to go along with the halving, you might see people running gpu farms for another year or so.