Do this and I guarantee your CTR will shoot up.. please post back with updates to let us know how it did..
1. In the top brownish bar where it says 'Recent Bookmarks' but an adlinks unit
2. Put a Large Rectangle ad under the recent tags box
3. Put a half banner after the 2nd bookmark posted (may require programming knowledge)
4. Move the top leaderboard ad under the search box
5. Get rid of the bottom leaderboard (you can only have 3 adsense ads, and my suggestions use up all three, plus, the bottom like that is a horrible place for an ad