You can keep track of people you like/dislike playing, strategies to use on certain tables, the phone numbers of hot babes you pick up from here, the number of hours you spent here instead of working or having a life, etc.

i already know i spend too much time here, i don't want to see how much! if people start blacklisting others it will get too hard to fill a table. someone might be angry one night but apologetic the next.

Well, I'm not talking about a blacklist, but more of a "do not trust this person at all" list. But that's just one of my examples; you could use the Play Notes textbox for whatever you want. Or, you can ignore it. All it would be is a little bit of DB space for text.