I think it's nice that there are cross network ads to have people find other SEs, but it feels to me like most of the skeptics ads are so offtopic that it detracts from the site itself:
(Jeff asked for examples): Are you looking for examples from skeptics in general or ones that have specifically been run as ads?
Plus there's a scale difference in offtopicness between "How do I beat this level in this game" vs. any one of the discussions on sexsex or religionreligion on skeptics.
If I see an ad for another site on the network I think "oh ok, this is a group of site for experts and I can apply these concepts to other things like DIY or making my own beer, cool, oh wait, a question about virginity."
Note: I'm not personally offended or anything, I just know that the Ubuntu community is a diverse place, and from scanning some of the questions on skeptics it's only a matter of time before one of those offends someone.