> If you accidentally buy 100000 shares of a stock when you meant to type 1000, you don't get a redo.

For the record, you might. Stock exchanges retroactively break many trades as "Clearly Erroneous".

[1] http://www1.nyse.com/pdfs/CEE_Policies_Email_Submission_Guid... [2] http://www.nasdaqtrader.com/trader.aspx?id=clearlyerroneous