This is kind of old, I wonder how it has progressed.
Personally, I'd rather deal with spam in craftier ways than prevent legitimate people from signing up.
Either you're offering a lightweight service with one single and simple functionnality (like instapaper.com for instance, which only requires a username for registration (not even a password !)); either you offer a multi purpuse service like github and if someone begins the registration process on a site like this and runs off because he doesn't want to fill a captcha.. maybe it's better he doesn't register after all.
Anyway what I really want to know is your numbers and how you got them :)
* Jane-Austen-Book-Club--The-dvd
* Download-Jane-Austen-Book-Club--The-movie
which works good enough as examples.
edit: the spam listings should be gone within the hour.
