uPortal 2.6 and later ship with the JA-SIG Bookmarks Portlet.
Configuration
The bookmarkSetName PortletPreference can be specified to name-space the bookmark set the user is interacting with. A bookmark set is automatically scoped to the user but one bookmarks set may be shared between multiple portlets used by the user if they share the same bookmarkSetName.
The portlet ships backed by an HSQLDB instance. You'll need to reconfigure it to use a real persistent database if you want to use this portlet in production.
Blog post with screen shots
Unlicensed user has blogged about this portlet, presenting a basic walkthrough complete with screenshots.