Not your mail
R5 provides the ability to incorporate "intranet" information with an employee's individual information (mail, individual calendar, tasks, etc.). That is fine, but that's not what an Intranet is for--keep that in mind. I don't want the company's intranet in my face except for when I want it. When I want it, I want it to be the way I want it--but out of the way when I don't. There should be a separate portal to the intranet from the employee's own information.

Intranet as community
Community is a component of any organization, and an intranet is an extension of that community. Keep this in mind when designing an intranet. If employees feel like the intranet is an extension of their own community they'll use it more and derive more value from it.

Collaborate
How could this be an article about Notes without mentioning collaboration? Collaboration is intrinsically connected to the idea of the intranet-as-community. Collaboration is a key function within any company. Employees really need to share and exchange information, knowledge, ideas, thoughts, and complaints; and be able to work together. Building this kind of functionality into an intranet enables an entirely new dimension to the value derived from the intranet.

Content
Content is also critical. Organization and structure are wonderful on their own, but useless without content. Successful intranets demand processes and plans for the continual update of key content within a site. This kind of updating must be mandated by the leadership of that organization and seen as valuable by the content providers and employees. The intranet, ideally, will be viewed as the obvious place for information dissemination within an organization, but only as long as the content is useful and current. This, of course, mandates incorporating the leadership philosophy of an organization into the design and processes of that intranet.

Fun
There's nothing unprofessional or wrong about making an intranet fun. In fact, it will help to increase community and bring people together. Consider adding a "Personality" section to your intranet where employees can create their own "pages" with their personal interests, photos, family information, hobbies, quotes, links, jokes, and so on. Make it theirs and encourage usage. Perhaps include a community resource section where postings can be placed about things for sale or rent, good restaurants, tips, good doctors, etc. Ponder putting up an inspiration page, a community calendar, birthdays, and anything else of general interest.