My neuro stated (and he does seminars for Tysabri) that their acceptable risk is 7:1000, so I don't think the company would start pulling patients off the drug unless there was a huge outbreak of PML.

Personally, as long as I feel good, I'll stay on it until something better/easier comes along. Mostly the better part! That is how I handled the interferons. I just want to stay the way I am today, and I feel Ty is the best med out there now for that prognosis IMHO!