Lots and lots of great info in this thread, and the bottom line is, what others have stated already...IT DEPENDS ON THE HORSE!
Get yourself a GOOD unbiased farrier who has an honest reputation. Beware of people who speak in extremes
horses need shoes, All
horses can go barefoot). If there's one thing I have found throughout my years as a horse owner, it's that extremes are usually incorrect because there are exceptions to EVERY rule.
My farrier is a good, honest experienced horseman, and he will tell me the day he believes my horse needs shoes. So far, that day hasn't come with this farrier yet, and my horse remains sound and balanced as can be. And we have Evented and have done Jumpers as well (albeit at the lower levels...I do admit I have not done high level with my little 14.2 hand mare, so I'm not going to say that she wouldn't need shoes if we did that, I just don't know since I haven't ever tried - it's certainly possible she would).
With my old farrier, at a different barn that had very hard footing, I did choose to put shoes on my mare, for the first time in her life, to protect her hooves from wearing down too quickly. After I moved to a barn with better footing, I pulled them and she's been barefoot since without issue. It depends not only on the horse, but on all of the outside factors that are acting upon that horse's hooves. Always stay open minded to both sides of the story.
Ever heard the funny saying "There's always 3 sides of the story...His, Hers, and the Truth"?
Well it applies to most things in life