I think, powershell is the best way to do configurations you have to do once. Adding some links to global (top) navigation is one of them:

asnp microsoft.sharepoint.powershell
$w = get-spweb http://takana
$l = New-Object Microsoft.SharePoint.Navigation.SPNavigationNode("Smells like team spirit", "/pages/teamspirit.aspx")
$w.Navigation.TopNavigationBar.AddAsLast($l)

Feature receiver

The alternative is to create a web scoped feature and provide properties:

Ziegler provides a cool intro, implementation sample and much more. When deployed we can apply this policy to a contenttype in the UI, or in code. To create our own expiration logic we have to implement IExpirationFormula and its ComputeExpireDate:

public class TaskExpiration : IExpirationFormula
{
	public DateTime? ComputeExpireDate(SPListItem item,
						XmlNode parametersData)
	{
		if (!item\["Status"\].Equals("Completed"))
		{
			return null;
		}
		var dt = (DateTime) item\["Modified"\];
		return dt.AddDays(30);
	}
}

In order to see IExpirationFormula, add a reference to Microsoft.Office.Policy (and maybe Microsoft.Office.DocumentManagement): To see our custom retention policy, we have to register it in xml, we can do it in Feature Receiver like Yaroslav:

A funny powershell command I came upon today together with my colleague. Remove all your custom features (which start with something, say contoso):

Get-SPFeature 
       | Where { $\_.DisplayName.StartsWith("Contoso.") } 
       | ForEach { Uninstall-SPFeature $\_.Id -confirm:0 -force }

Have fun!