Floating point data is displayed with scientific notation. You will see this, for example, in the Identify Results dialog box. In general, scientific notation is used to display the values in shapefile attribute fields which do not match the display definition of a shapefile field.
For example, consider a shapefile attribute field defined as Numeric, Width=20, Precision=18. Since 18 digits are reserved to the right of the decimal point, it leaves only one digit to the left of the decimal point (the decimal point itself takes up the width of one digit). A value of 1.123456789012345678 fits within this definition, but a value of 4321.123456789012 does not - there are more digits to the left of the decimal point than specified in the field definition. Scientific notation is used to display such values accurately.
To avoid having data display with scientific notation, ensure that numeric fields have appropriate definitions, and that the values in each field conform to that field's definition.