Well, it appears you just can't leave your doors open online. I left captcha off of my comment forms for as long as I could, but I haven't had a real comment in almost a year, at least not directly on my site, and I certainly haven't had a fraction as many as I have spam comments lately. It's not worth the trouble, I'm constantly being emailed now having to read how my useless blog is "Exactly the type of information" some robot is looking for and how much they appreciate my contributions and wont I please visit their porn site, etc.
I am strongly considering turning off comments entirely, really. I haven't had a real one in so long.