Well, research institutions or societies might be more willing than others to share their metadata. Here at the Lunar and Planetary Institute we want as many uses of our papers as possible. I've recently spent some time seeing if anyone would ingest our metadata. (Scopus might, ADS, GeoRef and a few others already do)
If anyone out there wants to add planetary geology metadata to their database just ask. I'd like to get it all OAI or available via an API someday. Sincerely, David Bigwood Lunar and Planetary Institute NB My address has changed. Please change your address book to the new address: dbigw...@hou.usra.edu Thanks