Can't add button to a ribbon

I was having problem adding a button to the ribbon. I've done this before and had no problem so I was kind of stuck. I checked if the definition in appropriate element.xml file was correct - and it was, however my previous custom action on another list was working fine. It turned out, that the feature adding "Custom actions" had a scope of "Web" and it wasn't active on this particular web. Problem solved :)

Configuring permissions on a list with powershell

Little of code:

$URL = "http://foo.bar" 
$web = Get-SPWeb -identity $URL/Workers/AbsenceReport
$list = $web.Lists["Absence report"]
$group = $web.SiteGroups["Visitors of the web"]
$assignment = new-object Microsoft.SharePoint.SPRoleAssignment($group)
$assignment.RoleDefinitionBindings.Add($web.RoleDefinitions["Contribute"])
$list.BreakRoleInheritance($true)
$list.RoleAssignments.Add($assignment)
$list.Update()

one thing: role definitions are localized, so in polish it isn't "Contribute" but "Współtworzenie"

Showing / hiding field depending on another field

I needed this kind of functionality:

I decide to use jQuery for this functionality. Here's how it's done:

1) jQuery was added to styles library through module

2) in my custom form in "AdditionalPageHead" following was added:

<script src="/Style Library/Scripts/jquery-1.5.min.js" type="text/javascript"></script>
    <script type="text/javascript">
        $(document).ready(function () {
            $("nobr:contains('Cel ')").append('<span title="This field is required" class="ms-formvalidation">*</span>');
            HideFields();
            AddEvent();
        });
        function HideFields() {
            $("nobr:contains('Cel ')").closest('tr').hide();
        }

        function getQueryString() {
            var assoc = new Array();
            var queryString = unescape(location.search.substring(1));
            var keyValues = queryString.split('&');
            for (var i in keyValues) {
                var key = keyValues[i].split('=');
                assoc[key[0]] = key[1];
            }
            return assoc;
        }

        function AddEvent() {
            var tmp = $("nobr:contains('Typ ')").closest('td').next().children('span:first').children('select').each(function () {
                var type = this.type;
                var tag = this.tagName.toLowerCase();
                if (tag == 'select') {
                    $(this).change(function () {
                        $("nobr:contains('Cel ')").closest('tr').toggle();
                    });
                }
                var fieldsetName = $(this).val();
                if (fieldsetName != 'Prywatne') {
                    $("nobr:contains('Cel ')").closest('tr').show();
                }
            });
        }
    </script>

Basically I'm getting things done in three steps:
1) add an asteriks mark to mark field as required (although I'm validating this through code)
2) hide field "Cel (tylko dla służbowych)"
3) if different option was selected inside "select" - show or hide hidden field