When is fixing your Mac just throwing good money after bad?

[iMore.com]

Does it make sense to fix my old Mac when it breaks, or am I better off buying a new one?

This scenario replays almost every time I go to work at the local Apple retailer: A customer walks in with an older Mac that isn't working right. It happens sooner or later with just about any reasonably complicated device you own, whether it's your car, your washing machine, TV set, or even your Mac. So what's the answer?

Full story from the iMore Blog...