There has been a lot of medical research into this and a lot of conflicitng advice - I read Dr Karl Kruzelnitski (sp????) on this and he reckons that all the blather about artificial sweetners causing cancer is rubbish. I tend to think of it like everything else - two kilos of salt in one go will kill you - but that doesn't mean you can't take a shake of salt on your chips - two kilos of artificial sweener in one go may cause cancer in rats, but are you really going to ingest 2kg of artificial sweetner in one go?

I still drink diet softdrinks - I just keep it to 600ml a day.