OnServerClick for button not working
<button runat="server" id="delete" class="btn btn-mini" title="Delete" OnServerClick="delete_Onclick"></button>

protected void delete_Onclick(object sender, EventArgs e) {
    ListViewItem listViewItem = (ListViewItem)((Button)sender).NamingContainer;
    if(listViewItem != null) {
        Membership.DeleteUser(((Label) listViewItem.FindControl("userName")).Text);
    }
}

<asp:Button id="delete" runat="server" CommandName="something" CommandArgument="somethingelse" />

protected void usersListView_ItemCommand( object sender, ListViewCommandEventArgs e )
 {
     switch ( e.CommandName ) {
         case "something" :
             // this is where you handle the button click
     }
 }

<asp:Button id="delete" runat="server" CommandName="something" CommandArgument="<%# Eval( "id" ) %>" />

 protected void usersListView_ItemCommand( object sender, ListViewCommandEventArgs e )
 {
     switch ( e.CommandName ) {
         case "something" :
             // this is where you handle the button click
             var itemid = e.CommandArgument;
     }
 }