The web is public, unless you make it private yourself. This is the best advice I can give anyone. Twitter, Facebook, blogs, comments, everything... consider them all public unless you yourself changed, or verified, them to be private via a setting. Be sure to read privacy notices also; just because something is not publicly attributable to your name your information and comments may still be used. We live in public (interesting movie coincidentally).
The web is very open, you can be quoted, re-tweeted, linked to, published in physical media, etc. Your articles can not be copied word for word (unless you use something like Creative Commons), but they can be moved around twisted apart and re-written on another blog; hopefully they will have the courtesy to site the source as you. Your photos, stories, and articles are automatically copyrighted (in the US at least), meaning you do not need to file for an official copyright on each item.
If you have a public RSS feed for your blog your content will be republished everywhere. Search engines index your comments about as fast as you write them. Information if fast moving and fluid and can be around the entire world in minutes. Unless you know otherwise, base your internet use on the fact that THE WEB IS PUBLIC!
This post was inspired by the story of Sarah Baskerville who thought her Twitter feed was private.