I do not wish to receive any unsolicited commercial email or unsolicited bulk email (spam). I get on average 4-5 junk messages a day (and several hundred real messages).
I never buy anything from a spammer. I never support a spammer in any way. I never reply to spam.
I never disguise (munge, forge) my email address. (I find it inconsiderate to people who wish to send me mail; if we break the way email works, spammers win.) This doesn't apply to email addresses that are actually mapped to more expensive or more intrusive delivery mechanisms (fax, pager, etc.). I regularly post to Usenet and to numerous openly archived mailing lists with my real address.
I always report all my spam, including spam I get through numerous mailing lists I am subscribed to (using Spamcop currently). I often call relevant parties in addition to sending electronic reports. I sometimes (rarely, because it takes time) place fake "orders" based on information provided in spam.
This is my service to all people who use email. I consider this service useful. (And I only spend seconds per day doing it.)
If you came here, you may be interested in my ideas on reporting spam and uce.el.