... sometimes it is basically impossible.
Especially if you have a GPU set to crunch GPUgrid tasks.
Basically nearly every single GPUgrid result returned is worth insanely more credits than the amount that 3 cores of my CPU and minimal credits from my Nexus 7 contribute. Take is as you like, but you must definitely get used to seeing credit distribution pie charts like:
But in the effort of saving a bit of cash, after having my main rig offline for a month, and viewing that power bill, vs, my most recent bill in which it ran for an entire month, it is about a $15-$20 difference in the cost of my utility bill. So needing to update it badly, I am pulling things offline for about a week, hopefully allowing the weather to cool off again before turning it on.