reason #652 I love LJ: notes. I use them when first adding someone so that I can check on how long we have been friends - if it has been more than 8 months and we haven't connected, I will probably take them off. Once I connect with people I make the note their name. If they are still new to me I will add several key facts because unless you use your face as your icon or regularly post photos of yourself, it's the key facts that are the link to memory.
On facebook I have added people from so many sources and I am often lost as to how we initially connected. Also I might forget who has done something terrible on FB, but on LJ notes save me. If someone is a raging bigot I don't want to accidentally add them again because they changed their default icon and I couldn't remember the name -- and re-adding someone I never clicked with after months and months is just awwwwkward.