Under WordPress v2.0.4, the rel="nofollow" attribute added to links inside the comments is duplicated whenever a comment is edited.
For example, a link inside a comment displays the following structure are the first posting:
<a href="url" rel="nofollow">title</a>
After the first edit, the structure becomes:
<a href="url" rel="nofollow" rel="nofollow">title</a>
After the second edit, the structure becomes:
<a href="url" rel="nofollow" rel="nofollow" rel="nofollow">title</a>
And so forth.
Fortunately, the rel="nofollow" attributes are visible in the comment editing interface and can be removed to return the links to only one rel="nofollow" attribute.
I have tested this with both my current configuration and under the Default theme with no active plugins.