How many money transfers do Visa or Amex handle per day? The Federal Reserve? What about Western Union?

Is bitcoin capable of doing 50% of that? 10%? 1%?

I know people have just decided to expand the block size but what's a realistic limit on how many transactions can be done per hour? Is that enough for real widespread use?

I can certainly see uses but I worry that he can never get big enough to truly matter. Or if it does that a government or large private entity could easily try to take it over through force of computing power.