Garry Smith from Winapp Technology wrote an excellent article on the SharePoint Advisor titled '4 Guidelines to drive SharePoint user adoption'. As he writes, user adoption is vital to portal success and continues further with the four key truths you need to understand and address to get users excited about -- and using -- your portal. I have met Garry personally here in Vegas and he is a good chap :-) with some very good advise for all of you starting your portal projects.
To do so, you have to set up this primary goal for your project: "Drive users to adopt SharePoint Portal as the authoritative place to complete all their information work." This goal means your general strategy will be to give users a lot of attention throughout the SharePoint design and deployment process.