I really didn't want to do it, but after over 150 spammy story submissions in under an hour, I've had to enable a captcha on the story submission page, as well as on the new user registration page. For now, I'm using the "simple" images, and hopefully that'll be enough to stop the spambots.
The captcha shouldn't be active anywhere other than those two pages; comment spam, while problematic, isn't bad enough to merit that move (and thanks to everyone who uses the Report Abuse link to point out the spammy comments).
Again, sorry I had to take this step, but I don't have the time to manage all these fake submissions by hand.
Mac OS X Hints