One of the key benefits of WPS is the 'supposed' interconnectivity of WebSphere Portal Server with all of those other IBM products that are floating about. You know, the Lotus Notes type stuff that doesn't always play well with others.
I'm sure the latest LifeRay would kick the latest WPS full released product's behind, as IBM is typically slow to catch up on all the latest trends. Having said that, WPS 7 will be out soon. A good friend of mine, Sal Pece, is doing some articles about WPS 7 at TSS if you were so inclined. (Evaluating WebSphere Portal 7)