I think it comes down to a level of responsibility, and trying to get past the egotistical angle that is easy to mistake. In my little world, we're pretty segregated in our sections of the code base. More than anything, when something goes wrong, I want to be held accountable if it's my "fault". Likewise, when something works well, I don't mind receiving a little praise..

If I am modifying existing code, for the love of bob comment vigorously, even if you don't sign your name to every line you modify, explain what the new code is doing.. Well documented code is a good thing!

cheers!