There are a fair number of people who write comments
and then don't check them for broken links or missing
end HTML tags or even basic grammar.
A suggestion to help this a little (and improve the quality
of the comments and to annoy the hell out of people
who post junk) is to force users to preview their
comment before they can submit. This is quite a
standard thing on a lot of forums.
In other words, when you first write the comment there
is no "Submit" box, only "Preview" - after you have hit
Preview then you see your comment.
The only change code-wise that would be required is to
remove the "Submit" button from the initial submission
No other changes would be necessary.