Latin -> UTF-8 - All or Some?

[dbv]

I'm planning on moving from an all Latin charset to UTF-8 on MySQL 4.1.

I have heard some conflicting recommendations on what to do so I was wondering which one is correct:

1. All tables/columns should be UTF-8 + Apache/PHP etc

2. The smallest column size should be used.

For example, if I have a table with 3 columns, "user-id", "username", and "full-name", if I follow #1, all columns should be converted to UTF-8, however if I follow #2, only "full-name" should be converted to UTF-8 since "username" will only contain ascii characters, and "user-id" will only contain integers. So a lot of space is saved by not converting everything to UTF-8.

For example, the username, "joeuser" takes up 7 bytes in Latin charset, but 21 bytes in UTF-8. So which is better to do, #1 or # 2, thanks for any advice on this.