For awhile now I've been running a 468x15 AdSense link unit after the first post in threads and the performance was surprisingly good for being so unobtrusive. Since I removed AdSense from the leaderboard and skyscraper in favor of more typical banner campaigns, I'm now experimenting with 468x60 AdSense after the first post, to keep AdSense on the page. If it performs just as well, I'll put the link unit back (no use having the larger sized ad if the smaller size does just as well). But if it performs much better, I'll keep it.