I'd go with what Kill said. Check the operator, they usually have different skill levels to sign up for, and a description of each. Just don't be that guy who can't ride powder who gets in the expert cat (happened to me before, the guy was not liked by the rest of the group).
I've been to a number of websites, most say strong intermediate level rider or better, just not sure how to interpret that. There was one company that said that they had 3 different levels, which would make it easier. I would think that some lucky folks would have had a lot of experience boarding in powder even at their resort due to where they live so the transition to catboarding/heli would be pretty straightforward, whereas others like me only get a day here or there of heavy snowfall, and never get truly deep powder.
For those who are in my situation and went out by cat/heli how difficult was it, and how experienced were you before you went?