I am looking to make some beer bread by substituting beer for water in some of my favorite recipes. I have heard that beer has yeast though, so I was wondering if the yeast in beer would work to ferment & proof my bread.   I was wondering if there is enough for say, an overnight rise without adding any extra yeast, or should I still use the full amount of yeast in each recipe that I use without the beer? 
Depends on the beer. In Germany we a beer called "Weißbier" or "Hefeweizen" which you can actually use for baking. The recipe 100ml "Hefeweizen" 15g flour 10g sugar => mix it => after 20h you have the equivalent of 25g yeast 