Let's analyze the situation.
There are mainly two distinct categories of users of a photos management system - producers and consumers. Each of them want different features from the system.
Producers have many requirements:
- Editability: Producers need to operate (rotate, sort, tag, etc) on the photos. Automatic or manual face recognition would be nice to have.
- Multi-user, networkable: There might be several producers (members of the family) operating on the same photos. They connect from different accounts on the same computer or from different computers (and OSes) in the same network.
- Search: photos organizations must be flexible enough to support both folders and "search folders" - based on search string.
- Publishing: enable consumers to view the photos over internet. The requires Sync or Upload to a web server.
- Comments: enable consumers to comment on the photos, rate them, tag photos and faces.
- Portability: no lock-in into some proprietary photos management system, OSS or proprietary. Practically this means that all meta data must be stored/duplicated into the photo file itself, using some meta-data format (JFIF, EXIF, IPTC, XMP, etc).
Consumers value different features than producers:
- easy and fast way to view the pics, preferably with captions (if any).
- they might want to specify filter that sorts out photos with nobody they know.
- ability to become producers (if allowed by host)
Use shotwell program (I am linux user) to manage the photos on a network share. The shotwell maintains a database for quicker lookup, which is located along the photos. All changes are duplicated in metadata area of the photos as well. Publishing is done to picasa web album (it properly renders UTF8-encoded captions and tags in the IPTC header of the photos). Picasa is used as publishing point only, disregarding comments, ratings or faces tagging (blocking these if possible).
The ideal solution would be in bi-directional synchronization of the photo files with some sharing-enabled cloud-based service, whereas the service embeds all additional meta-data generated by "consumers" into the files in open format. Clouds, are you listening?