Having a website/blog means there will be spam comments, just like having an email address means getting spam email.  I could very easily disable the ability to leave comments, but I sometimes like to hear what people have to say.  Currently, I have a very simple yet effective method of preventing spam involving basic arithmetic.  It works great at filtering out (a) people with math disabilities and (b) robots who leave spam comments.  Every once in a while, a spam comment gets through, either because it was left by a real human (which I find surprising, seeing that most spam is done by automated means) or because the robot happened to guess the correct number to type into the box. 

But what I find most surprising is how much spam I get while I'm away from my computer.  I spend a good 9 hours per day at a computer, so I can quickly delete spam comments that get through.  I might get one or two spam comments per week normally, if any at all.  But as soon as the weekend rolls around, I suddenly get three or four.  And if I'm on vacation like I was last week, I suddenly get all kinds of comment spam.  It's like the robots know when I'm not around, so they all gang up and abuse my website.  Be careful robots, I might disable commenting altogether.  Don't ruin it for everyone.