Hey Stephen- I think you are just somewhat confused.
Look at the rest of the comment tag. Do you see the hyperlinked words there Search Engine Optimization Seminar? This is called "anchor text" am I correct? Anchor text is looked at by search engines.
Anything inside a comment tag is ignored by the search engine. Comment tags are specifically for behind-the-scenes stuff. If they did index them, some of my sites would rank very well for <!--Header begin--> <!--Header end--> and <!-- Content goes here-->
I've seen other threads at other forums that pretty much convince me that comment tags are not indexed. People have run tests putting obscure words in comment tags on high pr pages and months later, they still are not found.
SO- using comment tags for their intended purpose (removing something from being displayed on the page) is perfectly legit.
Hope that helps clear things up for you.