Here's what good it is.
Hm. I've got a pair of OG Visiontek 4870's in an old Phenom 9850+ box that aren't doing anything at the moment ... I wonder if the reward in bitcoins is worth what I'd blow in electricity? Seriously - my i7 laptop paid for itself in about 40 days just in terms of the PG&E bill, never mind the productivity increases.