The first number is the number of cows and the number in brackets is the litres of milk produced since it woke up. 
Nice
I use poclbm.exe with the following command line:
The output looks like this:
xxx.xxx.com:1234 [353.720 MH/s (~362 MH/s)] [Rej: 0/3614 (0%)]
I'm referring to the numbers in bold.