Blog etiquette is becoming more and more of a hot topic. I frequently see people that are violating simple etiquette for blogs. It would be so much easier to be polite and follow a few simple rules.
One of the major rules I see people violate is that they decide to attack the person via comments on their blog. This is really not considerate. The person has spent their time, effort, and energy to create and publish their blog. If you do not agree with what they are saying, the more polite thing is to simply leave it be. Attacking others only makes things worse...
If you are going to spend the time to make a comment, make the comment meaningful so that it adds to the value of the blog. Blog manners would suggest that you should add something that shows additional ideas or thoughts to add in a positive way.
Some people have differing feelings on what is proper blog etiquette about leaving a link in the comments section. I believe that the right thing is that if the link adds value to the topic of the blog post, then the link is fine and in good taste. If you are simply adding the link to promote your own agenda, then I think it is wrong. When you "keep it real" and add value to their blog by posting the link, then you are doing a good thing. This should be a benefit to the owner of the blog when it is done the right way.
Copying content from others is bad blogging manners. If you need to take a direct quote, go ahead and do it as long as you give the original author credit. Nobody likes a thief (including me and my website), so write your own content.
Aside from that, use the golden rule and treat people the way that you would want them to treat you if you were creating your own blog. Of course, that really is the essence of manners and etiquette. When you are considerate of others and their feelings, you show others that you care and that their feelings are important too.