If you run a website that encourages user interaction of any kind, whether it's just through a contact form or through comments and forum posts, you're no doubt going to get a nice serving of spam. Drupal website are not immune to this problem? There are many different ways to deal with spam. You can choose to personally moderate every single comment you get, which will quickly get overwhelming as your website grows, or you can install a tool to help filter out the trash and leave you with less to handle. One of the ways to do this is to use a CAPTCHA, and you can customize who has to use it and who doesn't. I've implemented this as well as reCAPTCHA to enhance it.
On the comments side, I have now added functionality that allows you the option to subscribe and be notified when new comments are added to posts that interest you. Pretty cool, huh?
The full writeup on how this spam and comment functionality was implemented can be found at Managing Spam and Comments.
Don't forget to leave any comments, questions and such and I will respond to them.