ydobemos: The worst e-mail sin is putting the entire text of the previous e-mail
See, for me it is the other way round. While for private e-mail it usually doesn't matter, back when I was working as a data analyst I'd consider it one of the worst sins
not to include the text of the previous e-mail. I'd be emailing hundreds of customers and co-workers and nothing was worse than getting an e-mail like "Sure, that's a good idea. Include it too." from someone and then me having to dig and search for previous correspondance to see what they're talking about.
About bcc and cc, it really depends on the situation. Again at work I'd often have to e-mail person X and make them aware that people Y and Z are also kept informed of the situation. bcc'ing won't do then.