There was a web site a few years ago where a young US girl kept cans of diet coke at various temps for periods of time and then tested them. her mum had access to controlled temp storage gadgets. The breakdown products affected the taste.

I can't drink Aspartame without gagging.

We had "Zero" here in Aus a few years ago - wasn't very popular. It was caffeine carbonated water with Aspartame. No colour, no sugar, no odour, no taste.

We had a range 'sugar free' carbonated drinks here. The brand name I can't remember, but they had a 'Soda water'. The cute thing was that he brand name (can't remember it now) was incongruous when associated with 'soda water' which was just carbonated water...