Curly braces can be really hard to distinguish from parens because they appear in the same sort of place in e.g. JS, and IDEs and highlighters often render them in stupid low-contrast colours. I hate it aesethetically, but I get the usability need.

Hmm, my first reaction was the same as yours. But I have quite bad eyesight and looking at the "regular 400 at 16px" example on the page reminded me that I definitely sometimes find myself squinting trying to work out whether a character is a parenthesis or a brace (Droid Sans Mono). So I suppose it'd probably be quite helpful to have a brace that's very visually distinct from parenthesis even if it's not particularly pretty on its own.

Oh, it can't be that ba.... OMG KILL IT WITH FIRE! WE HATES IT!

--my actual reaction