While I didn't have any problems with smelly-gas, I did have problems initially when I started. I started off taking a bit too high of a dose, and my stomach was rumbly and 'off' feeling. When starting a probiotic, it's really important to ease into it and increase your dose gradually, kind of like with Acacia. While adding good bacteria is a good thing, your stomach needs to adjust to it. With these Bio-K bottles, I took 1/4 bottle for 4 days then went to 1/2 bottle. The first 8 days or so were tough, simply because I had started with too much without realising it.
Some probiotic capsules say to take 3/day. I would start those by taking 1/day. A soy yogurt probiotic is easy to start with one teaspoon and work up by teaspoons. I'm not sure with powders, but if you can take a small dose of it then that is best.
How long did you give the probiotics a try? And what kind of dose were you taking?