If you numerous people wanted to convert BitCoins to dollars when the boom takes a dive–does Mt. Gox have enough cash on hand to pay everybody?
No. Cash is regularly transferred from the various ways of getting money on MtGox to their bank in Japan. However, he does keep all of the deposits on reserve, so it could be sent out after a few days.
Moreover, if I wanted to withdrawal $10,000 worth of BitCoins and put the cash back in my Dwolla account, what percentage would Mt. Gox take?
I sincerely appreciate the information. Thank you.
First off, unless you've contacted MagicalTux with your personal information (I don't remember what's needed, sorry), you'll be limited to withdrawing $1000/day and $10,000/month due to anti-money-laundering laws. Otherwise, it's the standard fees. (0.67% to convert BTC to USD then 25 cents to withdraw)