A rather late update - apparently it does do wonders for your performance! 16% or so increase in exercise duration
I'll add some articles & a couple of study links. Way too much to copy & paste it all (& I'm watching the Ed Coan DVD set right now - I know, not the best idea to watch one of the worlds greatest powerlifters when you've got a recovering back
Anyway, the articles (a lot focus on the UK exeter study):
NHS (blood pressure)
The Exeter study (full text)
Effects with moderate exercise
Effects with walking & running
So, there you go a LOT of articles, but actually when you look at it very few actual studies. Most focus on one study (the Exeter study), simply because it had such a profound effect. I'd like to see some repeats, comparing one fruit juice with another & other variations to confirm that it is beetroot juice alone or a number of juices that may have a similar effect & to confirm the effect actually occurred of course.
Final note - if this pans out in other studies it looks like I might have to start getting beetroot juice whatever my personal taste is
if you're looking at 16% or so increases in training duration that's nothing to sneeze at!