[graeme]

There's some evidence that sweeteners harm gut flora. Here's a random study I found on splenda affecting the gut flora of rats:

http://www.ncbi.nlm.nih.gov/pubmed/18800291

[mistercow]

A panel of experts from multiple universities (including Duke, where the study originated) smacked that study down pretty hard: http://www.ncbi.nlm.nih.gov/pubmed/19567260