It's open source portal and comes with lot of out of box portlets.
Documentation is very good from Liferay 6.2.
It has very large community.
It comes with CMS tools also it let's you to integrate alfresco.
It provides SSO integration like LDAP, CAS.
It has great flexibility to organize Users, Roles, Sites.
It allows you to create website in minutes.
Developers need to have good skills which increases cost.
Few resources are available.
You have to purchase the license for enterprise edition which gives extra features as well as support.
Documentation still can be improved, it's difficult to do some things which should be easily achieved.
If any body want to build portal with CMS and User Management you can really consider this.
But you should keep in mind that human resources costs are high.