I am a GIS Specialist currently working at the Environmental Research Group Oxford.
I Have used TikiWiki on a couple of projects, check out he sites below and message me with your thoughts and tips...
IGAD LPI Data Portal - TikiWiki used as a data portal to Download GIS Data.
EDEN PhD Directory - A more traditional use of TikiWiki as part of a PhD community for a European-wide project with institutions and students all over Europe.
I would always be interested in getting involved integrating more Geo applications into TikiWiki. But due to pressures of work elsewhere I am unlikely to do anything unless asked!
Also Check out my other sites (not TikiWiki I'm afraid)...
EDEN Data Portal - This site was the "inspiration" for the IGAD Data portal above.