When I picked these up I was concerned about durability and comfort. Not anymore. If these are your first pair of barefoot shoes it may take some time getting used to them, but when your muscles adjust they are amazing. They're so lightweight you'll almost forget you're wearing shoes, then you step on a formerly run ending rock and realize that you are indeed wearing the Ultras.
I use them for just about everything. I have owned them for less than a month and so far I've ran five 10k's, daily 5'ks, hiked the narrows, use them as my approach shoe when climbing, plus the occasional around town stroll. The ability to use it as a water-shoe is sweet and works well. Ease of putting it on and taking it off make it great for any multi-shoe activity.
I own these and the Evo II; if I had to pick one it would be the Ultras. They are one of the best shoes I have ever owned. Straight up sick!
Update: Hiked the Zion Narrows and Subway in these and loved it. I removed the sock liners and just wore the outer, as anyone knows who has hiked the subway you're in and out of the water consistently for about 6 hours. It also includes some handline rappels and swimming. All I can say is that these shoes performed perfectly! The week after the subway I guided a group to Havasupai for a week. I did not use them for the hike in or out but the whole week there they were all I wore. Once again I love them! On a side note they also work great as a triathlon shoe because of the fast drawcord lace system.