A common complaint about SharePoint was the lack of security trimming in the URL. Several solutions were proposed by the community which involved client side scripting or ISAP filters. The next version of SharePoint has a SPSecurityTrimmedControl that can be wrapped around almost anything  it seems.

E.g.

<Sharepoint:SPSecurityTrimmedControl runat="server" PermissionsString="ManageWeb">

This should be hidden from everyone except the site manager<br>

</SharePoint:SPSecurityTrimmedControl>

The PermissionsString can contain a comma delimited list of  permissions from the following (unconfirmed and possibly incomplete) list

OpenWeb

EnumeratePermissions
ManagePermissions

ViewUsageData
CreatePersonalGroups
CreateSscSite

BrowseDirectories

ThemeWeb
LinkStyleSheet

UseRemoteAPIs
UseClientIntegration

EditMyUserInfo
BrowseUserInfo

BreakCheckout

ViewPages
ViewFormPages
WriteWebPages

ManageSubwebs
ManageWeb
ManagePersonalViews

AddDelPrivateWebParts
UpdatePersonalWebParts

ManageLists
ViewListItem
ViewListItems
OpenItems
InsertListItems
EditListItems
DeleteListItems
ApproveItems

ViewVersions
DeleteVersions

CreateAlerts
ManageAlerts