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. It's only part one of the Resident Evil 3 series he is working on, with R.P.D., Clock Tower, Hospital, Park, and Factory stages located somewhere in his to do list.
You can see screenshots of the mod, check out the development history, and download the beta version of Raccoon City Streets at Outatime's website below.
Beta 1.0 is now Live! [Outatime via Evil Avatar]