I talked to one of the guys I work with who used to be on the uPortal team. He said that they are big on WSRP, and that it's generally the preferred method of integration. eXo also supports it, as do Plumtree, Sun (through it's Java System Portal Server), IBM (through WebSphere), Vignette, BEA, and Oracle (among others). I'm told it's developing to be one of the preferred standards for portal integration in general.
