Automatic type conversion is my favorite. I can't even count the number of times I've received Excel spreadsheets where data was completely lost because of it. Leading zeroes at the beginning of your account number? Excel will gladly chop those off for you. Order number looks like a date because they used the year as a prefix? No worries, Excel will change that to a standard date and completely forget the original format.
Maybe I'm just crazy, but I don't think a business-oriented application should favor convenience that much more than data integrity.