Although creating a portal from scratch using java, XML, J2EE, or other programming tools is certainly not beyond the capabilities of an experienced web programmer, the time required is often prohibitive.
Many commercial products are now available to give the programmer a hand.
It is a very young and immature market, crowded with young and immature vendors. They are traditional Internet start-ups. Add to this dynamic the fact that many portal products are essentially the same, with very few differentiating features. Generation One portal products are characterized by a focus on content. Otherwise, they will need to settle for the limitations of a Generation One portal.