Is it viable to CPU/GPU mine popular cryptocurrencies given that they have dramatically spiked in value recently?
Taking Bitcoin as an example, a typical CPU is about 10,000 times less efficient than an ASIC (compare the Mhash/J numbers here vs here), so the cost to mine is roughly 10,000 times higher than the reward.  In the last few months, the price of Bitcoin has maybe doubled or tripled from $5,000 to $15,000, which is nowhere close to enough.  Check back when the price hits $150,000,000.  Assuming the difficulty doesn't go up by then, which it will.