I have a fairly small setup planned made out of spare parts essentially. - 4 computers each with 7970's, giving a combined hashrate of approx. 2.7Gh/s. The computers and cards are already paid for and don't owe me anything, and they are all located somewhere where I don't have to pay for the energy usage. Under these conditions (i.e. no overheads), I think GPU mining is still okay for now, correct?

I know I'm not going to be making as much as the big boys out there - but it's not much problem for me to keep these machines churning away 24/7.

I'm not so clever at the math in all this - but am I right in thinking that if the difficulty rate increases at roughly the same rate as the exchange rate, then nothing much changes? (eg. if difficulty doubles, it takes twice as long to get a bitcoin, but it's worth twice as much, so net gain/loss = 0). Or am I missing something.

Sorry if this is too basic, but I'm guessing this is what the newbie section is for.

TIA