I'm in the middle of an application for judicial review (application filed, response filed, now the last step of filing the request for a hearing due in a week's time.) At this point I'm much more optimistic of obtaining judicial review. From my own study, about 20% of applications are granted. I'd say that 20-30% of granted appeals are successful. Most applications are refugee appeals and thus FSW appeals have a bit better chance of review since they've not been previously reviewed.
Much of this really depends upon your attorney. In my case, my attorney had seen a situation that was very similar in which CIC rejected the application but cited grounds that were opposite of my case (and it was the same CIC officer making the decision.) No other attorney would have been able to provide that unique insight.
After filing a very good application I upped my estimate to about 40%. After the government's response (which was, to be honest, amazingly lame, arguing that I could just go apply in a different category and thus shouldn't waste the court's time - but completely ignoring the substantive grounds raised in our appeal) I've now put it at around 70-75% that I'll be granted review.
So I'll let you know how it comes out. Odds are still likely that the court will end up supporting my original FSW application rejection.