This module and the ad module?

One quick difference might be:

Classified will be shown for x amount of time
And advertisement runs on based on time, clicks or views of ad impression

I've write based on the written Features on http://drupal.org/project/ad

More over when I've used it lastly in Drupal 5 no. of click/views of ad impression was already there.

I believe the key differences lie in their purpose:

Ad Module is intended for advertising (banner/text) campaigns where performance of the campaign can be monitored through ad metrics. It is about page impressions over time, targetted to windows of time and geographic location if desired. It can be tied to nodes and taxonomy terms.

Classified Ads module is intended for site users to raise advertisments for a product/service/event/etc. tied to a taxonomy term (with a starting bias towards terms like For Sale or Wanted). Ads are for fixed periods, but renewable.

When I initially made a decision about which module to use on my own site I choose Classified Ads. I just want to let people post advertisments that last a fixed amount of time. If I had instead wanted to offer a service (possibly paid) where by users could do business advertising I might have gone to the Ad Module (I actually just use Adsense). And if I had wanted to start my own online store then I would have gone for one of the e-commerce modules.

I have flagged a Roadmap item on the project page (http://drupal.org/project/ed_classified) to explore the synergy and differences further. Right now, we have people using ed_classified who need this module maintained with bug fixes and a few obvious improvements. Down the road some it may be that ed_classified could merge into the Ad Module or simply grow further apart in differentiating. Time will tell, but there needs to be an ordered path either way. And that process should better answer this question as it's bound to come up.

Cheers,

Miles