I'm interested in learning from organizations that have set up online databases for listing people, their professional activities and contact information. There are questions on at least 3 levels, but first I wanted to go through some conceptual background and seek feedback on that.

The idea of collecting people's professional & contact info in an online database by permitting them to enter and update their own data is hardly new, and indeed is probably the foundation of the "social networking" sites that have enjoyed some popularity in recent years (and that some have recently been questioning the future of).
In thinking of a database project that would, among other things, seek to facilitate communication and collaboration among experts and activists on African localization, I'm actually reflecting on an online database of African studies scholars set up about 10 years ago that persists today but with outdated info. This example - and indeed the recent questions about the longterm viability of social networking sites - give one pause. Are such online self-maintained directories viable? Is the problem with the ones that become moribund that the (ongoing, thriving) networking aspect of the internet in general is not well harnessed in such delimited spaces? Or that it is unrealistic to expect a broad group of people to keep coming to the site and updating their info unless there is a specific incentive beyond acceptance that the listing is a Good Idea? Does anyone have experience in the lifecycle of such a resource where the outcome has been positive (that is, the database has ongoing utility to its members and reasonably current information)?
One idea that comes to mind is the possibility of building small interest communities related to a larger subject with the idea that such smaller communities might maintain themselves (i.e., the small virtual community consists of people who would probably interact more and know each other, hence providing an incentive to each other to keep up with the group), and that these can be accessible by all members of other small communities in the linked larger space (the latter being the hope of the project). Sort of the reverse of a Ryze or LinkedIn where you join the larger list and then perhaps sign on to a special interest group or two within.
It's along these lines that I'm thinking and seeking feedback, but there are also as mentioned above, questions on 3 levels re the mechanics of setting up an online database of people's contact info, for those who have experience in the matter:

1) Usability. What were the choices and evaluations of the choice in terms of software, approach, ease of use and set-up on the site, maintenance, and potential for users to maintain their own info? I'm particularly interested in FOSS solutions (cost, adaptability), but aware that one is likely to incur a cost to adapt a workable template to one's particular needs.

2) Security. Once you start to have interactive systems and/or list people's contact info there are a range of security and privacy issues. With the main aim of facilitating contact among people working in a certain technical
area, the kind of info would be limited, i.e., specific to the reason for having the database. And of course one can munge e-addresses to limit phish and spam issues (strictly vegetarian).  But what kind of site/dbase security issues are there - i.e., what sort of problems does this sort of interface regularly encounter - and what are the solutions/preventatives?

3) Linkability. If using such a database in tandem with other info on a site, how are links handled? This is kind of a vague question admittedly, but to the extent one seeks to link, say, project info and people/contact info across applications,

Any feedback to any of the above, including experience and recommendations would be appreciated.  Thanks in advance.
Don Osborn
PanAfrican Localisation Project