The 2.4 release has basic support for PDAs – see /portal/pda in your server – the PDA portal has its own style sheet:
/portal/styles/portalstyles.css
The 2.4 release also has the workgroup portal support as well:
https://source.sakaiproject.org/svn//reference/trunk/docs/architecture/sakai_workgroup_portal.doc
Sakai 2.4 also has support for RSS, Atom, and OPML:
/portal/rss /portal/atom /portal/opml
These show sites, announcements, etc – give them a try.
After 2.4 was release a bunch of features were added to trunk in /portal
Making the PDA portal optionally eliminate iframes – experimental feature
Hierarchical site navigation
I include some properties to play with.

# Indicate that default subsite behavior
# true – Include subsites unless the sakai-subsites property on the site is false
# false – Only include subsites if the sakai-subsites property on the site is true
# never – Never include subsites (post-2.4)
portal.experimental.includesubsites=true
# Indicate that where there is only one page viewable on the site –
# supporess the left column including the tool list and presense (post-2.4)
portal.experimental.maximizesinglepage=true
# Indicate the tool Ids that work with the PDA inline feature
# Add the String :debug: to indicate we want to see debug output in the log
# (post-2.4)
portal.pda.experimental.iframesuppress=:debug:sakai.createuser:sakai.motd:sakai.iframe:sakai.ifame.service:sakai.iframe.myworkspace:sakai.iframe.site:sakai.profile:sakai.membership:sakai.resources:sakai.dropbox:sakai.announcements:sakai.sitesetup:sakai.synoptic.discussion:sakai.announcements:sakai.synoptic.announcement:sakai.mailbox:sakai.news:sakai.messages:sakai.synpotic.chat:sakai.schedule:sakai.blogger:sakai.poll:sakai.calendar:sakai.siteinfo
# Only use this for testing
portal.pda.experimental.iframesuppress=:all:debug:
# Tools that do not work with the non-iframe portal
# sakai.chat (fails badly – too many frames)
# sakai.discussion (fails badly – too many frames)
# sakai.rwiki (preview fails)
# gateway site list – comma separated values indicating site IDs –
# these sites must include the .anon role and at a minimum give
# the .anon role site.visit – and any other permissions you want
# (usually *.read) permissions to the .anon role.
# if the .anon role does not have site.visit – these sites will not
# appear in the gateway – even if they are in this list.
# if this is not set, the portal simply displays a single gateway site
# specified by gatewaySiteId
gatewaySiteList=home,about,downloads
Normally, when users go to the URL defined by serverURL, they reach the
!gateway site (the site defined by gatewaySiteId). gatewaySiteList can
be used to present other sites, via tabs, to non-logged in users. By
default this property is not defined, so only the site defined by the gatewaySiteId property is shown to users when they go to the
URL defined by serverURL.
Sites specified in this property need to have the .anon role, and at
least the site.visit permission set for the .anon role, or they will not
show up as tabs to non-logged in users.