You are not penalised for low CTR on the content network, so unless you think that you are been attacked on the content network (to drain your budget or in passing by scraper sites) then I think the free publicity point is valid. I can get us much as ~1,000,000 content network impressions in a day for much less than 3 figures USD for example because of the HUGE difference in search and content CTR and I reckon that some of that mud sticks eventually!
So I usually run both content and search network.
Rgds
Damon
you can set up a seperate adwords campaign for the same terms, but only to run on the content network. That way your ctr wont be affected, but you'll still get the exposure.
As pointed out by Damon, the low CTR from content doesn't figure into the CTR used for calculation of your Ad Rank and your position. Only the CTR on Google's own site is used for that purpose. So that should not be reason at to why you need to split content ads into a separate campaign.
However in some cases I have seen that the conversion rates of Content clicks and search clicks to be different and hence need to be priced differently. In those cases I have split them into different campaigns with different Max CPCs for the adgroups.
So how can I trust my ad will show ok if all I can see is a too low CTR?...