I just started a blog a few days ago and I made a modification to the comment code to eliminate comment spam generated by automated scripts.
I added a mandatory human answerable question at the top of the form. This prevents automatic scripts from even making it to your editing queue which saves you from wasting time dealing with spam. I use the rather inelegant (lazy) approach of just killing the request on the processing page if the supplied answer is not "5".
Here's an example:
It might be a good approach to add this in the future. I might implement it like so...
1. In the admin section I would add this kind of option...
"Would you like to ADD, MODIFY or REMOVE a comment spam fighting question"
ADD - MODIFY - REMOVE
2. If they click ADD then it brings up a form that lets the user enter a question and answer which are written to the db.
Or you could just hack it into your code right now if you think it's a good idea. I hope somebody finds this useful.