I have 3 pair that I got on Ebay a couple years ago. I just had them out for "show and tell" at my weekly knitter's meet-up. Mine are made of pyrex (borosilicate I believe). They are pretty sturdy, but I'm sure if I dropped them on a hard floor they'd snap.
I have knit only a tiny bit with them - they are pretty slippery. Some people may not like the rubbing together of glass rods, but it didn't bother me. I got them more for the neato factor and for display 'cuz I'm a goon for tools and gadgets.