a security issue, feedbacks welcome

[Jeff]

Hey

asp.net 2.0

I'm creating a web site where users must login to access to secured part of
the site. When Logged in, the user can view a list of all the registered
users... each person's name on this list is their login name... I assume
this is bad, because then all the others can see what login name another
user is using...

When clicking on a user in this list, a page opens viewing this persons
public profile. When the user clicks on the user in the list I add this
user's UserName as a parameter to the URL... -> Default.aspx?user=noob... I
guess this is bad, but I'm not sure my workarround is any better: replace
username with the users Id in aspnet_Users table..... I could use POST, but
I've read POST is slow

What is your thoughts about this?

Jeff