The laws to prevent spam simply don't work. The Act that was supposed to prevent spam from the U.S. is rightly referred to by spammers as the Can-Spam Act. Apart from making millions of people think that spammers are operating legally (which often they aren't), it has helped tirck millions into giving their email addresses to spammers by using the opt out links, which may get you opted out from ONE spam campaign, but makes you a nice confirmed email address which may be used by the same company or sold to other spammers.
Anti spam rule #2: - NEVER click on the remove link in spam emails.

European law is no better. It specifically refers to personal emails, although as Justin from SpamAssassin says "Actually, this is based on the transcription of the laws in each country; I think we may have fixed this in the Irish transcription. at least, when a business receives spam, the recipient may indeed count as a "person" hence make it prosecutable.
Of course, none of the governmental agencies in any of these countries can afford to spend much on enforcement. lobbying is still required there."

WARNING #2: If you or your ISP or host (who you received email through) uses a blocklist, it is POSSIBLE that some legitimate emails won't get through. This is unlikely with the Spamhaus (sbl-xbl.spamhaus.org) or Spamcop (bl.spamcop.net) blocklists, though Spamcop recommend that people use it's list only to TAG email, not to reject it because it is an aggressive list.
Some blocklists (like the one operated by http://ordb.org/) block all known open relays - these are vunerable servers which are open to abuse by spammers, but may also be being used by legitimate customers (i.e. you!). They issue this warning: "While we try to limit that connectivity loss to only IP-addresses that are currently running open relays, sometimes a spammer hides in and amongst nonspammers in order to share a more positive fate with those nonspammers. What actually happens is that the nonspammers share an unpleasant and negative fate with spammers in that case. In other words, if you are not willing to accept occasional blockage of legitimate email, then ORDB is not for you. That being said, it would probably be worth having a look at our testimonials page."

WARNING #3: While most anti-spam blocklist are legitimate, there is at least one anti spam blocklist (SPEWS) which deliberately targets non-spammers.
At the time of writing SPEWS blacklisted over 900,000 people in the UK because some people who used the same Internet Service Provider are/were spammers. As they don't block emails themselves, they might seem unimportant except that some Internet Service Providers DO use their list and some people are foolish enough to use an anti-spam program with SPEWS enabled. If so, you could lose important emails.
CHECK with your ISP Do they use the SPEWS blacklist (as opposed to more reputable ones)? If so they may block important emails sent to you which you want (or in some cases NEED to receive.)
Spews choose to target whole ISPs, and call the innocent millions affected (900,000 in that one case alone) as "collatoral damage" - their words not mine. It is their policy to use their attacks on the innocent to blackmail ISPs into getting rid of the spammers. They also provide NO WAY to contact them except through a newsgroup populated (at least in part) by the same kind of extremists as they are. Use that newsgroup if you've been blocked falsely and you will probably suffer abuse and possibly be threatened with everything from physical attacks, hacking, or denial of service attacks. In my case, even though NO reputable blacklist listed me (and even SPEWS didn't claim that I was a spammer) some idiots from that newsgroup made allegations which had my sites taken down. Being legally trained it only took me a short time to convince the host to restore them, others might not be so lucky. Unlike SPEWS, who hide behind addresses in Russia, most hosting companies ARE answerable to the law.
We all think spammers should be ousted, but is it ethical to knowingly and deliberately attack the innocent and to use them as a weapon? No. This is why few reputable anti-spam organisations have anything to do with them.
As Justin of Spamassassin said "nobody who understands spam filtering would use them (SPEWS) to filter real email. Even our own mailserver is blocked by SPEWS"
I would like to congratulate Catherine of Spambouncer. Although we are both against spam, we had a rather bad-tempered diagreement about Spews in which we were both probably partly at fault. In spite of her saying that she wouldn't read anything I had to say, I can only assume that she has as she, like most reputable anti-spam sites, no longer recommends spews.