Regarding some of the ideas you mentioned and Simpy:

- people discovery – example:http://simpy.com/user/otis (look at the right side, scroll down). Those are people related/similar to user otis. The same can be seen for any user with enough bookmarks to make the connection.

-search other than by tags, you’ll see that Simpy has the richest search content, syntax and functionality of all social bookmarking sites out there (I’m one of Lucene developers and search is my big love). You can do +this +that, this AND that, this OR that, this NOT that, +this -that, “this that”, this* that* and so on and on….
What is even nicer, is that all of the above can be done against 1 or more or all searchable fields. What fields are searchable? Title, nickname, tags, description, and FULL-TEXT!

- regarding closed workgroups used for research – Simpy already has this! Take a look at the Groups functionality. Private or public, closed or open, etc. I’ve been using Groups to collaborate with people in various ways: with my book co-author about a new edition of our book, with several people interested in Social Bookmarks and other Social Software (interested in an invitation? let me know), and I even have a group for sharing stuff with my family! Quite handy, I find it.

Ok, that’s all from me for now. Good post, keep it up!

just to quote a hip-hop bling…’what else can I say to you (…) ‘.
Your blog is awesome. You still keeping a high-profile.

Take care.