I've been begging dh for some from Namaste for my birthday. They are beautiful and pretty and I want them! I would imagine that unless you throw them or drop them, they would last fine...And the glass would knit so beautifully, I would imagine...so smooth and warm. And it would feel "softer" than my aluminum needles.
Also, I have been eyeing these needles: http://www.shopknitch.com.
Not glass, but they are certainly unique and pretty. Love the wood choices!