tedster - 10:54 pm on Oct 25, 2010 (gmt 0)
Meaning you cannot repeat the same keyword in anchor text over and over and over. There's no exact percentage to share - whatever it might be at any given time is variable and seems to depend on the average practice in your niche.
But you have to be way over the top to run into this problem. If you can look at your page like a normal visitor it just jumps out at you. Natural link text would not look like this.