For my university (manchester, UK) I started a map / wiki interface
for students to make a geographical guide for other students to POI's
like bars, shops, etc.
The code started as GMaps code, and at the moment I'm transferring it
over to OpenLayers and eventually OSM support.
You can see it at  See  for a brief description of the
functionality and various views you can do. (don't miss the Edit pane
accessed from the top left).
The map there is a bit buggy, i've improved it since, but not updated
the live version.
Everything's fairly object orientated, so
maintaining/extending/adapting it should be easy.
Very brief features:
*In the split screen view clicking on a marker shows you the relevent
page in the wiki panel of the page.
*Users can add, edit, move, delete markers.
*Map view can be filtered using collapsable checkbox tree to show/hide
*Catagories can be edited by users.
*There is a change list of all changes made by users (see Recent
Changes link on Edit view)
*If users are logged into the adjoining Wiki, any edits by them on the
map are recorded as by them (and if you want to restrict edit access
to only logged in/certain users, you can do that)
This isn't the best solution possible, and depending on how much OG
will interact with OSM, it will need to be adapted heavily.
I don't know what the OSM guys have thought of along these lines, but
just telling you in case your interested!
I'm going to try and come to the OSM/OG meetup in Oxford (Starting a
new job the weekend before though).
A few licensing issues for it;
The checkbox code is from blueshoes.org
, and free licensed for
non-commercial use, but not distribution . I couldn't find any
F/OSS checkbox tree code, it looks like Dojo might have a f/oss
solution  now though with an extension to their tree widget. (I'll
code this in if you guys are interested).
I got a few tips from various gmaps tutorial websites, I'll need to go
back and check their licenses (may of been cc-by-sa). I could code it
all again myself now (and will if i need to), having learnt the facts
from them. I'm note sure of the legal situation.