Web Portals Defined

What is a web portal, and what makes a good one? Here's the definition from the Webopedia:

Commonly referred to as simply a portal, a Web site or service that offers a broad array of resources and services, such as e-mail, forums, search engines, and on-line shopping malls. The first Web portals were online services, such as AOL, that provided access to the Web, but by now most of the traditional search engines have transformed themselves into Web portals to attract and keep a larger audience.

And here's the definition from Neil:

A portal site leads you to other web resources and sites, by organizing the destinations -- a launch pad. Many companies with a collection of web properties tie them together through their portal page. The major portals offer customization (e.g., my.yahoo.com); other portals select information based on a topic.