If you've tried probiotics, what was your experience regarding availability, cost and effectiveness?

I went to the grocery thinking that there were several yogurt brands offering probiotics. I only found one brand, Activa. I’d be interested if anyone is taking the Activa challenge where you eat 2 a day for 4 weeks with a money back guarantee. (I didn’t exactly get what they were guaranteeing.)

Have you experimented with probiotics in another form? Powder or pills perhaps?

Advice to anecdotal evidence…let’s hear it.