The ability to run Android apps in Ubuntu mode is well supported. Also sharing of data (pictures, movies, contacts) seems very seamless as well. It even integrates with the telephony stack of the phone, allowing the user to use SMS, make calls, or use the phones' data connection in Ubuntu mode.
I would actually say that for an alpha product that has been just announced, it seems very well done.
By the end of the year, we will have dual core ARM Cortex-A15 processors in high-end phones, far more powerful than the current generation of Cortex-A9s. Such a massive jump in performance will unlock many new usage scenarios and running a full desktop environment on a phone a might become a reasonable possibility. Motorola's Webtop has shown that there is great interest in such a concept, but Moto's implementation suffers greatly from limited functionality and lacklustre performance. A full Ubuntu desktop running on a high end Cortex A-15 smartphone might indeed prove an interesting concept, and provide a useful differentiating factor for an OEM.