I notice a few sites do that. I have actually clicked on some myself in some sites just because of thinking that it was the sites navigation and not the actual ads. Once I do the first click then you can see that it is actual ads as you see the horrid Google design so I then click of it. I wouldn't think putting link units right next to the navigation would be a good idea. This is because the navigation is used so that people can navigate your site and not be tricked into clicking ads, where they will end up going of your site. I personally don't use link units and never have. I have sometimes clicked on ad units, but never have clicked on the second page of one link unit
I held off trying them for a long time, because I didn't think they would earn me anything. I was wrong. Put them at the end of an article, and people sort of naturally click them. I've also had success tucking them in spots on my blogs where there wouldn't be room for much of an ad block.
i put link units on top right hand corner blended well with the top navigation above and the left navigation below it... they seem to attract attention due to the niche of the page im putting it on...even if its ads they click the 2nd page, if the user finds it useful, they will just click on it... they won actually hear the $$ (chikeching) sound generated to us ... they are more interested in the products and services that they are looking for... less space, nice magnet like topics, simple, neat and lastly efficient...