There some problems with your code for WP User Front End. On a site like ours with more than 600K users, these functions could effectively stall out our servers. If you have more than a few hundred users, this plugin is going to start hurting.
The code makes a lot of unnecessarily expensive calls to store the entire user database in an array.
1. wpuf_list_users – this function attempts to load the entire user database
multiple calls to this functions from other areas in the plugin
2. wpuf_show_users – attempts to pull all users in a separte wpdb query, then run through a loop to display them all in a list