I'm considering setting up an account at Mt. Gox to accept bitcoins as payments on my web site. I'm wondering about the actual fees that are required to convert those to dollars and get them into my U.S. bank account. Their merchant page at https://mtgox.com/merchant says this:

"Never be forced to handle a single Bitcoin with our Instant Sell function and cash out into sixteen different currencies"

Say I use this feature and I list a product at $100.00 USD. I'm assuming they will display that along with the equivalent bitcoin amount. The customer pays that. Now is there exactly $100.00 USD in my account or has some fee been deducted?  Or did the customer get charged a fee?  If not, how does Mt. Gox make money?

Now once dollars are in my account, it appears that I can transfer them to a Dwolla account for only 25 cents per transfer and then from there to my bank account for free, is that correct?

Why doesn't the Generate Coins option in the client survive a restart/reboot?  It gets cleared when I restart my system each morning and I have to remember to go turn it back on.

Has Bruce Schneier ever commented on Bitcoin?  I searched his website but didn't find anything.

I just become aware of Bitcoin this week watching "Security Now" at Twit.tv. The main question I have about the system is why was 21 million bitcoins selected as the final cap?  Why not something more "round" like 100 million or 1 billion?  And why such a relatively small number?  I understand about the 8 decimal places giving you essentially 2.1 quadrillion tradeable units.  But the general public is not used to dealing with more than 2 decimal places in their currency. If the system took off to even the size of PayPal alone, a single bitcoin is going to be worth some huge number and we're all going to be buying things priced at inconvenient amounts like 0.00023, etc., right?