If you take pics for your blog or for personal use, you should have a read through of this.
The main points:
You are allowed to take pictures of anything as long as you are in a public place.
Owners of private property can ask you to not take pictures, and you must stop, if you are on their property.
No one is allowed to take your film/camera accept a police officer with a warrant, or if you are getting arrested.
Really the only way someone can legally stop you from taking pictures in public places is a police officer, and in most cases he needs a warrant.
It's good to know your rights.