You may have noticed that your FeedBurner service frequently includes "comment" links in the bottoms of people's posts, and that most feeds include "comment-url" fields that you could use to generate "comment on this" links rather easily. It would be even more spectacular if, when you have such data, you could go ahead and generate such a link for me and put it in the footer of each item. In the absence of this data, a simple link to the originating URL would suffice nicely. Either way, a link at the bottom of the post would be at least as -- if not more -- valuable as the one at the top.
Aside from making me happier, this could also help provide you with another metric of usage by your users. You'll know which posts they commented on, and can provide them a list so they can check up on them later. It seems to me that knowing the level of interactivity users have with specific sites would be a rather valuable addition to the amount of data you amass on each of your users, allowing you to target advertisements just that much more accurately.
This simple addition could go a long ways towards making my -- and undoubtedly countless others's's -- time with you just that much more pleasant. Not to mention that it would make each and every one of us just that much more valuable to you as a statistic.
Hopefully yours,
Oh heck -- like you don't already know who I am.