Here's an excellent example of someone using the Left 4 Dead creation tools for their intended purpose - recreating Resident Evil 3's Raccoon City.
You'll have to forgive the frame rate, as mod author Outatime is still ironing out the bugs for this faithful recreation of Raccoon City in Left 4 Dead, but it's obviously well enough along that he's seen fit to release the beta 1.0 version of Raccoon City Streets to the general public..