If you do a search on GoogleBowling or Bombing you will find some interesting reading on the idea of hurting other sites by playing with links and anchor text. From where I sit if you can shoot yourself in the foot then you for sure shoot someone else in the foot. A lot of it has to do with the site / age / vertical space / from what I have read. Google is looking for patterns that is the best it can do, if you change the pattern of your site or any site then a flag is going to go up - what happens next depends on the sites history etc. This would be a pretty easy theory to test if you wanted to invest some money and time at your competitors expense and I would guess it happens.