Spamming is the abuse of electronic messaging systems to indiscriminately send unsolicited bulk messages, the term is also used to describe similar abuses in other media like blogs. Spamming remains economically viable because advertisers have no operating costs beyond the management of their mailing lists, and it is difficult to hold senders accountable for their mass mailings.
I understand why people spam. There is a profit in it. I use multiple email accounts for various reasons. Currently I commonly use four. Each account has it's own purpose. One I use for purchases/trades, one for forums and newsletters, one for writing to government representatives and online petitions and complaining about product/service/business practices, and one in which I use for things online that I expect to get spam like surveys. I also use bugmenot's temporary 24 hour email address for things I expect to get spam but never want messages from. I started with only one email address but later added the others. While they were originally added for other reasons, such as a requirement of using the service or add-on to the service, I came to find it more convenient to use multiple accounts, each for a different purpose, than sub-dividing the accounts using folders and filters than to put everything at one email address. Of these email accounts the one that I expect a lot of spam gets a lot of spam, the one with purchases gets quite a bit, the one with forums and newsletters gets barely any, and the last one has not gotten any since I've begun using it (though it's annoying bulk folder keeps grabbing stuff that isn't spam).
Of the spam I get most of it is for viagra, sex, weight loss, Canadian pharmacy, lotteries I did not enter, and fraud like update account information at a bank I'm not a member of or they are going to send me money if I accept a deposit from them. I wonder how many people fall for these? Some people have to else, even with little cost in sending spam, there would be no point in doing so. Just based on the subject line you'd think that people would not open and click these emails. The tricks with fake lottos you did not enter shouldn't work, since if you never entered these lotteries how is it that you could be the winner? Get a free laptop and such should not work since everything has a price, it's just not always obvious as to what the price is. Fraud in the form of asking for personal information should not work since just about every place you visit online will tell you that they do not and will not ask for your personal information via email. The ones that I can see people falling for the most though is unsubscribe links in spam messages since the person may think they will stop sending them (and are legally required to via a federal law in the USA -CAN-SPAM Act of 2003). Really though clicking the unsubscribe link will often make it worse since they will likely log your information if you click the unsubscribe link, by clicking it you are proving to them that you opened the message and were willing to click on links provided in the message.
There are various websites and agencies in various countries that you can report online scams and spam to. In the case of banks and paypal you can report the spam to the bank or paypal and they will then report it to the authorities. I wonder how many police officers in various countries spend their entire shifts just tracing spam/online scams?
A good forum on spam and fraud is http://www.419legal.org/ It is a forum where people post information about emails or scams that they perceive as fraudulent.