eMail-Address and Parent eMail-Address (if COPPA-User)
Style being used
Homapage URL
ICQ, AIM, MSN, Yahoo IDs
User Titel
Join Date
Last Activity
Date/Time of last post
Number of Posts
Reputation Level
Various settings
ID of Avatar being used (if not custom)
Flag for showing "You've got a new PM Popup"
Language being used
Number of total and unread PMs
Birthday
Now, if this table is shared between various installation with the methode posted above (which ist of course possible) there will be a lot of problems.
For example the post counter:
You make 1 post in board 1, but as board 2 uses the same table it will also show 1 post .
Or the Style. the User might chose to select style 1 on board 1 and style 2 on board 2 - this isn't possible.
And so on and so on ...
I've just take a look into phpBB user table, and found out that it holds similar information.
So similar problems will occur.