Really? I would've thought due to the generally extremely low immediate profitability of mining coins (especially when you factor in electricity costs) these days would have caused more people to hold, in the hopes that the price of a coin will increase in the future. Otherwise the profits won't be high enough to justify mining in the first place. That's basically what I've been doing, and it has worked really well for me.
There is nothing wrong with holding, but it is my opinion that represents only a portion of mining (of all coins).
Mining Monero on a CPU right now is break even somewhere in the neighborhood of 0.10 USD/kWh. So for people with low electricity costs (and that includes people with electric space heaters who have an effective cost of 0 -- it was noted earlier in this thread that with declining temperatures in the Northern Hemisphere we would expect to see more mining), CPU mining can be quite profitable.
Nobody really knows the cost structure for botnets, but it isn't zero (it takes time and/or money to create and maintain a botnet -- they don't just appear out of thin air).
