Just got back from Liferays European Symposium in Frankfurt.
Great conference and great people - I can really recommend the conference to everyone interested in Liferay. Have been listening to many great presentations, including Sami's presentation on "how to build Liferay portlets with Vaadin".
Liferay comes built in with tons of really nice content publishing and web 2.0 type features. It defines a solid base to build communities and web sites/portals on. Because those features are more and more required by the business applications - we see Liferay Portal also as a perfect platform to build enterprise applications needing those features. With Vaadin based portlets for the "application like" parts and mixed with portlets what ship with Liferay Portal.
Besides the fact that Vaadin has supported Liferay for a while now, you may have noticed some subtle hints about something going on between Liferay and Vaadin, such as this, that and maybe even this. Because we see that Liferay and Vaadin are perfect match for building enterprice portals, there will be even more integration coming up in future. Core developers of Vaadin and Liferay are actively working together with Liferay to make the products work seamlessly together.
Update: Sami put the source code online for the demo application he created during presentation.