Ditto, you don't want to trade pinkies on margin. If it crashes they will call you at any moment and you'll be stuck with the bill.
I trade NYSE on margin, stocks that only require 50% equity. The chances of an established stock on the NYSE crashing 50% before I can get out is slim, although still poses risk. But I always keep cash in the bank to cover, just let it accrue interest. I trade margin because like you said you can get in and out multiple times (if you have over $25k).
If you have under $25k you can't make more than 3 round trip trades in a rolling 5 day period.
Don't trade pinkies on margin man...way too f-ing risky.