[wp-hackers] filter the_content without affecting the_excerpt

[Braydon]

Using a "the_content" filter to add a shortcode sounds like the cleanest 
way.

the_excerpt() is an inflexible template tag to begin with, in order to 
modify it's output length, and other parameters, you need to add a 
filter that applies to every time the function is called, where it may 
only be necessary to modify it once, not on every instance the function 
is called.