I wouldn't do it, but thats just me I guess. If you do it by accident well of course you can't take it back so there's no point stressing. But if I were consciously making a choice I would choose not to. As far as I know it has to do with the temperature of the machine, how well its cleaned etc. And you can't guarantee that unless you work there, or cleaned it yourself. As far as I know they use regular milk :-k Also keep in mind listeria doesn't affect everyone all the time, just the elderly, pregnant women, and those with low immune systems like cancer and AIDS patients. I always check before ordering a thick/milkshake whether or not they use soft serve icecream or tub icecream. Yeah you might be pretty unlucky but I wouldn't take the risk.

*hugs*
Cailin