Specific post sections per category

I’m not sure how to explain myself, but here goes:
Because WordPress 1.0 now has the ability for each entry to be filed until multiple categories, it would be interesting if each time someone clicked on the link pertaining to a specific category, it would only show the part of all posts that actually had to do with that category. For example,
/*example post*/
January 17, 2004 – What I did today – posted at 2:29 pm
<!–cat_books–>
Today I read Moby Dick…
<!–end_cat–>
<!–cat_movies–>
Today I watched My Big Fat Greek Wedding…
<!–end_cat–>
/*end example post*/
After clicking on the link for a specific category, say, for the category Books, all that would show up would be:
/*example category page*/
January 17, 2004 – What I did today – posted at 2:29 pm
Today I read Moby Dick…
(read complete entry)
/*end*/
This isn’t really necessary but it would allow each category to be very specific and make better use of the multiple-category-per-entry function. Maybe this is already available? Thanks.