[CentOS] Best practices for the maximal length of user names

Hello,

are there any best practices for the length of user names?

I tend to limit them to 8 characters and to follow the pattern 'first
letter of the first name'+'first 7 letters of the last name' (e.g.
mbaudier).

But people are sometimes frustrated with having their last name
truncated and I wonder if limiting the user name to 8 characters is
not a kind of superstition coming from some old times...

I would be very interested to hear opinions / experience about this.
(I'm using CentOS 5.5)

Thanks in advance!

Mathieu