For my own baking and cooking, I do my best to use vegan sugars. Beyond that, I'm one of those people who don't think it's reasonable to fret over the source for the sugar in every single other product. If someone goes to the trouble to make a vegan dish for me but uses regular sugar, I'm hardly going to turn my nose up at their thoughtful gesture.
As a listener of the VeganFreak podcast, I remember they discussed this exact topic once and came to the conclusion that with store bought or pre-prepared foods, it's just not reasonable to know the source in every case.
From what I've heard, not even
all white cane sugar is processed using bone char. If that's true, then without clear information on the packaging, how are people to know which is which? To expect a waiter or store employee to be able to specify seems like it'd be asking for a bit much, realistically.
I think the topic of sugar and sweeteners for vegans tends to be a bit gray, and differs from person to person. Maybe someday there will be more demand for clearly-labeled vegan (cane) sugar, but until then, things like this will be a hot topic for vegans.