just used my whiskey stones with my Left Coast straight tube. i'll definitely concur with Steve that they do not get cold enough. you can sense that the vapor is slightly colder but after using ice with smoking bongs in the past, it's not as cold as i feel it should be. when i've used ice with bongs, back when i smoked more regularly, it was like hitting cold winter air. even on the very first hit, the whiskey stones provide kinda cool vapor. i'm sure the SC glycerin cubes would be able to cool vapor down much more effectively.
also, the fact that i'm putting four 'stones' down my glass tube makes me just a little uneasy. no matter how gently i put them in. still a nice gift from my girlfriend though lol.