Most of you have probably seen the comment card at restaurants, hotels, and even from shopping at your favorite stores. Sometimes you even get a discount on future purchases for filling out the card. What these businesses want is feedback from those who do business with them. They want to know if their current service meets your needs, if something you would like is missing, or even if the service was below standard so they can fix it. Comment cards and soliciting feedback from clients is a necessary part of business, so much so that they will even give you an incentive just to tell them what you think. Comments from clients help a business refine their products/services and get the necessary feedback to retain current clients and attract new ones. 
Much as a business solicits feedback through a comment card, bloggers request feedback through the comments section of each post. A blogger is looking for the same thing: refining their message to retain current readers and attract new ones.
I've been mulling over this subject for a week or so, ever since reading Chris Garrett on New Media's article about improving your overall blogging by reading other blogs and commenting. In fact, his message is that you should comment on more blog posts than the day before for an entire week as an experiment to prove him right. Comment with valuable input, not just an agreement. His message is that by doing this you will actually improve your overall writing and develop your "blogger's eye" for finding the point of interest in a story. By generating discussion, providing good feedback, and getting involved in posts instead of just passively reading, you will bring richness to the community and your own blogging style. Chris actually advocates reading a lot of blogs and commenting in a substantial way before you even begin your own blog. Read the followup article here for additional incentives.
After reading Rich Jacobson's post on Givers and Takers I decided to stop mulling and start doing. Besides reading ActiveRain subscribed blogs, I also get RSS feeds of other blogs (Soundbiteblog, Bloodhoundblog, The Real Estate Tomato, Copyblogger, and several other personal favorites). Because of the ease of the RSS feeds in reading my favorite blogs through my email, I have noticed a drastic reduction in the number of comments I provide. This is really due to sheer laziness - I have to actually open the link to the blog to comment.
This week I plan to comment in a meaningful way to both the ActiveRain blogs as well as my other favorites. If these bloggers don't know my opinion to what they have written, how will they know if their message is getting through? For that matter, don't I want my readers to let me know what they think of my articles?
So, my challenge to you is to do the same. Fill out the comment card when you gain valuable information from a blogger. Let them know you've been in their "store" and what you think of their "products." You will gain a better understanding of what they have provided to you by actively responding with quality content and the blogger can continue to refine the message for maximum impact and exposure.
And who knows, maybe you'll get a coupon on future purchases at your favorite BlogMart.