The format string attack on printf you mentioned isn't specific to the "%x" formatting - in any case where printf has more formatting parameters than passed variables, it will read values from the stack that do not belong to it. You will get the same issue with %d for example. %x is useful when you want to see those values as hex.
As explained in previous answers, %08x will produce a 8 digits hex number, padded by preceding zeros.
Using the formatting in your code example in printf, with no additional parameters:
printf ("%08x %08x %08x %08x");
Will fetch 4 parameters from the stack and display them as 8-digits padded hex numbers.
%08x means that every number should be printed at least 8 characters wide with filling all missing digits with zeros, e.g. for '1' output will be 00000001
That specifies the how many digits you want it to show.
integer value or * that specifies minimum field width. The result is padded with space characters (by default), if required, on the left when right-justified, or on the right if left-justified. In the case when * is used, the width is specified by an additional argument of type int. If the value of the argument is negative, it results with the - flag specified and positive field width.
From http://en.wikipedia.org/wiki/Printf_format_string
use 0 instead of spaces to pad a field when the width option is specified. For example, printf("%2d", 3) results in " 3", while printf("%02d", 3) results in "03".
Source: Stackoverflow.com