@supernova - are your current blog, wiki, forum, groups all from one software? Or are they all independent but bridged together?

The benefit of something like elgg is that you can keep it all together very easily and the different tools are easy to integrate. For example, with 2 or 3 lines of code I can show how many blog posts a user has made when they post a comment in a group discussion topic. I could even show a link to these blogposts or even show a mini list of their titles as links.

But if your tools are all independent, this would probably be a lot harder to do. However Alexander is right. If you have a vintage system that your users know, understand and are accustomed to, changing to elgg now might not be a real benefit. Play with elgg, see what you can do with it. The point about elgg is that although it's a turnkey opportunity the real magic is in being able to easily hack it apart and reassemble how you want it. Dr. Frankenstein would be over the moon if he wanted to build a social networking site. 

Ask your users what their thoughts are and get a little feedback from them. After all the customer is always right.

One aspect of social networking is content filtering based on the rather fuzzy notion of "friendship".  Bob is shown a blog on the BP oil leak because his friend Larry recommends it.  Or, he gets to see a World Cup video because Larry has posted it.  Now Bob and Larry may be friends because they are both concerned about environmental issues and they both play soccer on weekends, but these are kind of all under the cover of the "friendship" umbrella.

In a typical organization, information is structured and people play some specific roles.  Information access and flow are tied to the roles.  You wouldn't want to see a buget report because your friend churned it out; even if you would, it would be considered counter-productive from the organization's view.  So I think social networking is not particularly valuable in such setting.  Now an organization may have a social network site to promote commradeship and what not, but that's a different story.

One aspect of social networking is content filtering based on the rather fuzzy notion of "friendship".

It's just one aspect of conent separation and aggregation in SN. "Friends" in common aren't content-delivery channel, but more - method to quicky access. Search, free-taggings (and tag-related search) in another, more powerful and independent practice usable for any tasks