I get a LOT of emails from a variety of industry sites that I opted into, but I admit that many go unopened. Well, this morning from Jakob Nielsen's Alertbox, I received one with the title "Does SharePoint Destroy Intranet Design?"
Being chest deep in the planning stages of a few SharePoint intranet projects, it was worth the look and it paid off to help clarify some thoughts our team has been batting around.
Whether you are building a public website or an intranet, it does boil down to understanding the users and their unique goals. There are some distinctions that Nielsen points out that are important when planning your intranet design.
There are some unique considerations to factor. In most companies, your employees already have a good level of understanding about the company and its structure. Outside audiences usually don't have that benefit out of the gate.
The difference may seem small, but to the outside world, your company needs to "tell a story" where for the employees it is often about disseminating information, collaborating on content/documents, or performing core business functions. The way this should be structured is quite different.
Leveraging the internal understanding of organizational structure, culture, and core needs allows for a more utilitarian approach allowing employees to efficiently accomplish their tasks.
One big challenge though is just sheer volume. Look at your public site and then your intranet...the latter usually is and should be substantially larger due to the need to provide business value beyond publishing basic company/product information. Intranets are not "destinations", but rather should become indispensible tools for your employees.