In the book "Intranets for Info Pros" (Information Today), there is a list of seven elements to consider when considering a portal implementation, and I think they bear repeating here for anyone looking to either build or enhance an intranet portal:
1. Limit technical customization of the portal to items planned for by the software supplier or easily accommodated in the software.
2. Fully understand the logic of how the individual portal software approaches content publishing, information architecture, and collaboration spaces before designing the portal--in other words, do not try to radically adapt the portal to your preconceived notion of how it all should work; use the software's design to achieve your goals.
3. Do not underestimate the time and effort of content migration.
4. Avoid duplicating the problems of the old intranet in the new portal by working with content owners to migrate content item-by-item rather than page-by-page (try to break content into distinct individual content items rather than relying on the old page structure).
5. Map the individual content items to individual portlets or content modules (use a content inventory listed on a spreadsheet), and then assign content modules to pages--fully understand and take advantage of the distributed nature of portal content publishing.
6. Be sure content owners and their organizations are prepared to take on content maintenance before beginning the migration process. Emphasize that starting with a simple set of content is a good thing--complexity witll come soon enough.
7. Recognize that content migration is a golden opportunity rather than a necessary chore; you will never have a better chance to clean up out-of-date content and navigation again.