Plans for a D7 version of the Spam module, and possible alternatives? I am thinking about porting an existing D6 site to Drupal 7. The main shortcoming that I see is that the splendid Spam module is still missing for Drupal 7. 

I don't want to relay on third-party services, so I wonder whether there is any plan to port the Spam module to Drupal 7 and if not, what alternative spam filter can be used for Drupal 7.
I think you were looking for an antispam module, weren't you? Try Mollom.

It kills comment, contact form and registration form spam, has image and audio CAPTCHA service.

Try it, it is made by Drupal core developers.