I should have posted it earlier. For bloggers suffering from spam comments, it's time to cease your nightmare!
On January 20 I installed MT-Keystrokes plugin in hope of stopping spam comments. Guess what? In the past month I haven't got a single piece of spam comment! It used to be bombed by about 20 spams every day. MT-Keystrokes works so well that from time to time I even start to suspect whether comment system on TIMELINE is functional. I love the idea of Simon Goodway so much!
A simple way to reduce comment spam without affecting the reader's experience is to make sure that every comment has some level of human input. As Simon suggests, by validating that the user has entered keystrokes while entering a comment (using javascript), we can effectively weed out any robots that bypass the comment form altogether.
Automation is one of the most fascinating pros of computer products. It's also the downside that can easily be taken advantage of by vicious users. Seems the most effective way to stop abused automation is to require more human efforts to lower the level of automation. In this sense, MT-Keystrokes really turns spammers off. I am a little bit concerned [ what a worryart! ] that spammers will find a way out to bypass the anti-spam mechanism but at least, we are on the right track now.

Do u always get spam comments? If not, just delete them. Really need to install another software?
Junking spam comments is not the most effective way to get rid of them, let alone when you've got to deal with more than 20 spams every day [ and they are growing at a very fast rate.] Deleting spam comments is a relatively passive means to solve it; what we need to do is to actively prevent it. It's of extreme importance to let spammers know that we are fighting back and don't take advantage of us.
Also, if you are as zealous about MT as I am, installing an MT plugin and tweaking some template code is no big deal at all. I enjoy that!
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