Should I use a user's id instead of username even when user id requires extra work?

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MySQL

game

I am making a bot for Skype which will operate as a narrator to a huge zork-like text-based game.

In my "users" table, I have user_id and username and so forth, but this user_id is something I have generated myself. In the end, the username is always the one that I will have to use to find the user_id of a user since every message in the chat program can only give me the username of that person and not the user_id that I have invented myself.

This means that every time I want to modify a users data in a table I have to use the username to find the user's id, and I do this because the user_id is the only thing mentioned in many of my tables rather than the username.

My question is of course, should I skip all this user_id crap and just use the username?