Vaadin On Liferay is a site dedicated to promoting Vaadin portlet development for Liferay.
Liferay has a long list of benefits... There are functional benefits (i.e. security and authentication, a long list of out of the box functionality) and there are non-functional benefits (i.e. it's a widely used platform, it is open source, it runs under many application containers and databases, etc.).
Why Vaadin on Liferay?
By combining all of the benefits of Liferay with the ease of creating RIA portlets using Vaadin, a powerful foundation emerges for developing a responsive portal platform for your organization.
If Vaadin on Liferay is so great, why hasn't it taken off?
Personally, my opinion is that it has never been completely clear how to get started using Vaadin on Liferay. The Vaadin website goes to great detail talking about how to use Vaadin for servlets, but it only touches on portlets as an afterthought. Liferay portlets can be created using so many different frameworks (i.e. JSP, JSF, etc.), they can't cover every option completely nor do they want to appear like they're taking sides on which framework is the best, and they spend more time covering the internals of the portal and how to use it effectively.
So if some samples are put together to demonstrate how to properly do Vaadin on Liferay, it could become a dominant player in portlet development.
This site will provide those samples, the details, and some tools to facilitate using Vaadin on Liferay.