Thought I'd throw my two cents in...
Whatever probiotic I'm taking/trying out, I always take more than the recommended dose at regular 6 to 8 hour intervals. This is because I've noticed that a little digestive relief throughout the day helps more than relief just in the morning or evenings. I prefer types with a variety of bacteria, the more the merrier! I've tried keiffir and other probiotic drinks, but my body likes capsules better, probably because I'm semi-lactose intolerant. Cultured dairy products like keiffir, yogurt, and cheese don't hurt me as bad as normal dairy products. I'm not sure if this really makes a difference, but I also try to take my probiotics an hour or two before eating. Gives the bacteria time to migrate to my intestines before the digestive juices start to destroy them is the theory there.
I'm currently taking Florastor, and VSL #3 which I just started a couple of weeks ago. I'm happy to say that it seems to have helped reduce the number, severity, and overall grossness of my BMs. Both are pretty pricey, but I can either feel less crappy and be broke, or save a few a bucks and feel and act crappy. I tried using some cheaper pro-bs, but none of them seemed to do anything.
Good luck in your hunt for a probiotic.
Diagnosed w/ moderate UC in May '06, had symptoms for years prior to dx - currently flaring
Asacol, Florastor, VSL#3, Wellbutrin XL, Prozac, multi-vitamin, and fexofenadine for allergies