Aaron D. Campbell

Expire Comment Links was inspired by <a href="http://yoast.com" rel="nofollow ugc">Joost de Valk</a> 
in an article he wrote called 
<a href="http://www.searchcowboys.com/columns/764" rel="nofollow ugc">Comment links: an experiment</a>. 
It all started when Matt Cutts talked about how Google changed how it handles no 
follow links in his article on 
<a href="http://www.mattcutts.com/blog/pagerank-sculpting/" rel="nofollow ugc">PageRank Sculpting</a>.
No one knows for sure yet if this will be beneficial or not, but for those that 
want to be on the cutting edge and try this experiment for themselves, this 
plugin automates everything.
Requires PHP5.
You may also be interested in <a href="http://wpinformer.com" rel="nofollow ugc">WordPress tips and tricks at WordPress Informer</a> or general <a href="http://webdevnews.net" rel="nofollow ugc">Web Developer News</a>

Expire Comment Links

Allows you to stop displaying links for old comments. PHP 5+ required.

Blogestudio

Pau Iglesias

Show a warning message in admin header area when your blog visibility is blocked for search engines.
Also, when your blog is visible for everyone, hides the de-indexing option to avoid accidental changes.

Search Engine Visibility Warning

Show a warning message when your blog visibility is blocked for search engines. Also, hides the de-indexing option.

Expire Comment Links vs Search Engine Visibility Warning