As I mentioned in the previous post I've been using free classifieds.  To see the extent to which free classified sites get indexed by search engines, I placed ads for my main work-at-home site at quite a few of them.

A week or so later I searched Google for "cheap online and offline promotion", which was the heading for an ad I placed.  Three of those ads appeared on the first page.  So, clearly those particular classified sites are getting indexed, and fairly quickly.  Not sure of the proportion of the entire sample this was, but it's not insignificant. 

So, I'd say it's worth it.  The problem is: which classified sites -- aside from the biggies like Craigslist, which dominate the search engine rankings -- do you place your ads at? 

There are two options: you could use a scattergun approach and be certain that a certain proportion will give you some link-juice and/or clicks. 

Or, you can do searches for various keywords related to your niche and look for free ads appearing in the results.  Then place an ad at the classified sites that appear.

Or you could combine the two approaches, which I think is the best option.