JohnTP has an article on the 5 reasons you are losing your RSS Subscribers.
Oh, wait.  Number 2 is Re-Blogging.  Damn it!  There goes another reader.  (bye mom!)

1. Infrequent Posting

   If you suddenly stop posting for a while and then post only with apologies for not posting, it’s a sure way to lose subscribers. If what you post is worthwhile and valuable, your readers won’t mind infrequent posting, but when you do post remember to not post apologies.

   If you really must apologize to your readers, do it at the end of a valuable post.

2. Re-Blogging

   If your blog only consists of copy-paste work from other blogs, then you are encouraging your readers to click the “unsubscribe” button. Re-blogging is one thing you must stay away from. If you are doing it now, stop it before you learn the hard way.

3. Constant Negativity

   I have seen a few people blog when in a bad mood. They post irrelevant to the content of their blogs. While this is ok when done rarely, you can lose subscribers when done often.Think twice about posting if you are in a bad mood, depressed or have nothing to say.

4. Treating your readers like idiots

   Talking down to your audience and treating them like idiots will send them right to the “unsubscribe” button. Prevent such posts in your blog.

5. Bad Titles

   Subscribers must be able to make out what you have posted from the title itself as most of them jugde whether to read the post or not from it. The post title must be a very short sumary of your post.