It’s pretty bad, I have to say. It’s not just the washout but the reflections. Unfortunately there’s not a huge difference between the new retina screen and the older versions this way. Personally I would much rather have had a matte low glare screen than the extra pixels, but Apple is all about shiny these days.
This is with the old ipad, but the new one isn’t a lot better. Here I was inside a fairly dim room and you’re just seeing the reflections from the sliding glass door behind me:
So I’d say what you’re going to have watch out for is when you’re in shade but the building behind you is catching the sun higher up, things like that.