provide better support for microsites
It's often necessary to provide several "presences" within a single Plone site. This can range from providing adhoc small variations and distinctions in the look and feel to establishing a completely new navigation root. In large scale organizations there's also a difficult choice to make between providing one big Plone site or numerous smaller ones, with pros and cons to each. There are lots of solutions, but no smooth route to implementing this microsite model with sufficient flexibility to take into account this range of use cases.
Lineage has solid releases and does this quite well now.
There is a buildout that you can test drive lineage with here:
AdminAlexander Limi (Admin, Plone) commented
Look into Lineage, new add-on product that works with Plone 3.3. Should solve a lot of these issues.