Creating a WordPress plugin that will modify wp_users?

Is it ever OK to create a plug-in that will add a new data column to a core table like wp_users? I’ve never created a WordPress plug-in before and I’m feeling the need to make one for BuddyPress. This plug-in would need to tie a specific bit of data to specific users on the site…so if modifying wp_users is not OK, then should I just create a new table that will store the user’s ID and the data that I want attached to it instead?