Probiotic dosage?

For those of you who supplement with probiotics, how much do you use and how do you take them? Do you combine them with certain foods, take them at certain times of day, etc? Do you also consume foods contained active bacterial cultures in addition to this supplementation like yogurt/buttermilk/kefir?

Also, what symptoms have you all noticed improvement from, if any, when using probiotics?

Thanks.