It might be brilliant, but as Alex Barnett points out in his post and as I have identified in a prior post as well, use of public online services for tagging/social bookmarks and RSS feeds also can present a risk in terms of security and competitive intelligence.
AARF employees have learned to add the tag 'AARF' when they come across a web page (using del.icio.us), a photo (Flickr), or a news story (Digg) that they think will be of interest to their colleagues. Shortly after they add this tag, the bookmark (look at the top of the box), thumbnail of the photo (middle) or headline and description of the story (bottom) show up within the AARF E2.0 Intranet. So AARF has found a fast and low-overhead way to let its employees share Internet content with each other. It's also free; these interfaces with del.icio.us, Flickr, and Digg require no fees and no permissions. I find this simply brilliant.
Source: Andrew McAfee
Alex's post is well-worth reading. Tagging schemes are important for groups to agree upon so they can work collectively around a project or other activity and maintain a shared cognitive model (one that is loosely-coupled and cooperative in manner). Tagging has a lot of value in this regard. Unfortunately, for groups to maintain some type of organization and cohesion, tags will likely reveal insight into the business activity. Tags are a form of social annotation and can be used be used as a form of short-hand and dialog. A tag could read "important_for_company-abc_deal". Mining this information could very well benefit competitors. If the online service has a security level to restrict access, that might help, but then IT groups need to assess the provider as they would with any hosted offering (e.g., web conferencing).
That said, I am a proponent of tagging and social bookmarking systems. I would also recommend that people read Andrew McAffee's full post here. There are a lot of interesting points made.
For intranets, larger organizations might also look at the open source Scuttle technology. I am aware of a large enterprise that has downloaded and customized that software to work within its environment. A more public example of an organization using tagging/social bookmark technology is Connotea. Enterprise software will also emerge in this area. IBM has been extensively covered in the media regarding its dogear and Fringe efforts. These tools are being used internally at the moment but I expect enterprise-grade product to emerge from IBM based on their internal experience (with the needed secuirty and identity controls).
The point here is (1) the "irrational exuberance" around Enterprise 2.0 from a technology perspective (I actually agree with the organizational dynamics aspect of the meme) should not act as an excuse to forget about security and risk factors (2) online services can deliver real value in certain situations but organizations need to assess their use just as they do with traditional software.