I always wonder about people like you. How do you manage your receipts for all these things? And what about the additional time to go back and return lightbulbs. Does that not more than cover the money you save from the bulb?

Not the original commenter, but:

Not difficult. File folder full of receipts, sorted by "action" date. Cost of gasoline is trivial (~$0.20/mile). Time doesn't cost anything (if you wouldn't otherwise be working).

>And what about the additional time to go back and return lightbulbs. Does that not more than cover the money you save from the bulb?

Err, you just bring them with you the next time you go to the supermarket...