stock/unpersonalized LOR

[lalabooks]

Besides "how well you are able to perform in graduate school," what are grad schools looking for in a LOR? I guess my question is when professors have so many students to write letters for, even when giving them all your information and selling points, I'm afraid all letters will sound stock and unpersonalized. Just FYI I graduated undergrad in 2006 and am about to complete a year and a half prerequisite classes for grad school. So I haven't had a big opportunity to get to know these professors personally. I am planning on asking them soon but the above is a concern I have. Anybody familiar with this?