LDAP implementation for web app

Hi All.

I've had LDAP implemented in a web app I've been working on for a while now. Basically the way I had been doing it was taking the username entered and generating the DN by "cn={username},ou=blah,dc=blah,dc=com", and attempting to bind.

This worked fine, but now I'm trying to interoperate with an ldap server in which the username is not actually part of the DN. When a user attempts logon I am now doing an ldap search with "(uid={username})" to obtain the DN and binding.

First question: how expensive is this? Would it be worthwhile for me to only do this once and then store the DN to be referenced on future logins without doing an ldapsearch, or is this not worth it?

Further: This particular server allows me to search ldap anonymously, but its conceivable that some servers will require me to bind first. How do people typically implement this? Add a dummy user to LDAP which only has read access to the directory? How do you handle storing the password for that dummy user in a secure fashion?

Thanks!