When I worked at Hewlett Packard back in the late 90s, I was told that HP had the world's largest intranet. I'm not sure how true that is, although I did find this press release from 1996 where they make that claim. I do know that all groups in my division were expected to create and maintain an internal website. That website was in turn linked to department websites, division websites, etc. Employees could also create their own websites & link them to their group's website. I was the admin for my group's site.
It was a great tool for three specific reasons:
Information Repository - While I was there, our group started using the website as a convenient way to store information online. Plus, guess which is easier: a) Tell someone to go to your group's website, click on "documents", and download the test report; b) direct them to H:\Shared\public-files\bfg2000\documents\reports\new-test-report-v1.1.doc
Reasearch - This was back before Google was commonly used (although I was partly hired because my manager had found me online via Google), and Wikipedia wasn't even invented yet. There were search tools that HP had specifically for digging up info on it's intranet, and you could find a lot of technical information that way. I downloaded bits of code, internal specs, and other useful bits of info that HP employees had loaded onto the intranet.
Status Information - Testing schedules, group members, who is working on what project, milestone schedules. All these things were listed on our website. Managers could go there directly and get that information without bugging the engineers.
Flash forward several years. I read an interesting article in Wired magazine about company blogs and sharing information while on a plane flight to Denver. When I got back home I talked with my company's CEO about starting up an internal company website that would include blogs and other information from the various departments. I had some success - by partnering with our IT manager, we introduced Sharepoint to the company and got people to start using it.
At my current employer we use Sharepoint extensively, and it's a good tool for the three reasons I wrote above and then some. Other good reasons for having this sort of tool include a) it can be used as an inexpensive document revision tool, b) postings can start discussions about technical issues, and c) you can post general information (HR policies, company calendar, etc.) there.
I guess what I'm trying to say is this: if your company doesn't already use a tool like this, talk to your manager, director, or CEO about getting one.