Do probiotics survive digestion?
When I took Microbio we had a entire lecture on this. My professor's view was that they do not survive due to the pH of the stomach.  He told us that there are microbiologist on both sides as to whether they do make it to the intestine (or enough of them to make much difference) or that they do survive and help. I have added a link below to a article by the American Society of Microbiology. Here it is saying that it may be helpful, but that more studies are being conducted. 

http://cmr.asm.org/content/16/4/658.short