Here's another idea for a project that has been on my mind for a long time.
It's basically an opensource del.icio.us clone with some additional features that may be useful for enterprise environments.
The deliverable for this project is a server-side engine for companies to host themselves (or pay someone to host it, like the many hosted corporate wikis offerings out there)
Enterprise-specific features may include: enhanced user profile info/metadata, Microsoft Active Directory integration for user sign-on, department/project segmentation for link visibility (security profiles), links and tag suggestion based on company departments or specific projects/groups.
And just like any other half-decent idea, someone else has already implemented but none at the time of this writing seems to fulfil my requirements:
Scuttle (http://sourceforge.net/projects/scuttle/) is an opensource implementation but does not offer enterprise features.
ConnectBeam (http://www.connectbeam.com/) targets the enterprise and has many features, but is not opensource.
This could fit the opensource-but-with-paid-customization-services business model quite well.
If you're interested, check this idea's microPledge entry.