When is Blur Good in a Photograph

One of the rules of photography is not to have blur in the foreground. The above photo does. I've broken the rule. Since background blur is usually what you want in a photo, it's the most common blur photographers want to achieve.

Wherever the blur is in your photographs (there's usually some somewhere in them) let it have a purpose.

Here's some good reasons to have blur:

1. In the background when a clear object is in the foreground. This makes the object appear if it's popping out.
2. In the foreground when it makes a subtle pathway to a clear subject/object.
3. To show speed. In this case the blur will be trailing an subject/object.
4. To show something turning/spinning. Someone's head turning around while the shutter on a camera is open for a bit.
5. To light variations as result of an image taken with multiple exposures. For example, to get the feeling of what the eye would see when walking in New York City's Times Square.