I was getting dozens of annoying spam comments daily until recently when I installed Anti-spam plugin. It was easy to install and so far appears to work well - it rejects spam comments but lets real human comments through. I hope it stays this way. My main concern was false rejections i.e. not allowing valid posts. So far, this does not seem to be happening. It would be interesting to know how many fake comments were rejected. (It is possible this info is available somewhere but during my quick look I did not see it.)
Overall, Anti-spam plugin is a great time-saver!