Just a note from my experience with 3.2.5. Changes to the user table (at least in 3.x) such as adding additional columns are a BAD idea. Certain parts of the code do a 'select * from users' and then union/intersect. I added an extra column at one point to the users table and found that other modules broke in interesting and non-obvious ways. Then I got to have the fun of dropping and recreating the users table. It was ugly, and of course I hadn't backed up recently enough. :(
This is not to say that you CANNOT add a column, just that you should be aware that adding a column can cause undesired consequences in modules you've never looked at.
I'm still working with 3.2.5, having not enough time/energy to upgrade my mind to 4.5. Things are pretty snarly in there in spots. Changes to the core data model are probably not a good idea.
