Actually yogurt is somewhat regulated, if they are a part of the National Yogurt Association and they have the "live and active cultures" seal (gets into the billions when you have 1/2 cup, usually more than most probiotic supplements). http://www.aboutyogurt.com/lacYogurt/
But most products are not regulated, but food sources are a terrific source of probiotics, especially if you get a quality type. I also buy kefir and often they identify several probiotic strains and though they don't tell you the count, when it has a chance to proliferate, it will, provided they don't heat treat it (pasturization is done before this process). Plus, the calcium helps the probiotic to gain ground on the intestinal walls. The other benefit of buy a probiotic flourishing in a prebiotic (its food source) is that it has a chance to digest it and makes our disgestion easier and other benefits from this metabiotic. Sauerkraut and pickles in salt (not vinegar!), also should contain probiotics, if they are not heated afterward and even some sourdough bread.
Most of these probiotics should be able to handle the acid in the stomach, but not all can, nor can I tell you off the top of my head which cannot [edit: even H. pylori, the bad guy that can cause ulcers in the stomach remains there and DanActive is suppose to help, at least to a degree]. It may even be worth opening the probiotic capsule, if you are taking supplements as well, and add them to a cool food (yogurt, kefir, etc.) or drink, that way it gets in your throat and sinus for overall health. And the longer the bacteria are exposed to a food source, the greater there numbers can increase. However, I am thinking the enteric coated probiotics are more sensitive to the stomach acid or some other reason; since we are all primarily concerned with colon, this makes sense that there could also be benefits in trying this option as well.
Blessteve, good idea on adding kefir to milk, that way you can choose your own source and it saves money. Raw milk has the added benefit of the enzymes and other "stuff" that is supposed to be good for us and would normally be killed in pasturization.