As a broad rule, I trust no one when it comes to investing my money.
In this specific case, it is not necessary to trust the man. I suggest focusing on the logic of his positions. I listen to a lot of people. Its hard on my ears, and sometimes harder on my ego, but I try VERY hard to listen to all the viewpoints I can handle. Then I let these ideas have at each other in my mind. When one party starts making a lot more sense than another, I follow that view in setting my investment posture.
For example, a few years ago the gold bugs started making a hell of a lot of sense to me. So however nutty it seemed to go along with these "trilateral commission", "illuminati" kooks, I bought gold and it has done well for me. Someday, they will not make so much sense, and I will drift out of gold. At least that is my plan.
Back to Soros, I would point out that he has been essentially correct in his views for the previous few years. The dollar is going down. Check! The U.S. has fallen in love with the "markets", the Fed has abdicated its responsibility to supervise them, and it will end badly. Check! The housing market was fueled by excessive extension of credit, and its a bubble. Check!
So is it such a tremendous leap of faith, to see that he sees these things as getting worse before they get better?
Sure the guy has an agenda. But does he make more sense than the "just a tiny dip and we'll be done!" crowd? I believe yes, and that is what I focus on.