the number is 1000. WHY? “This is because Active Directory defaults to 1,000 as the maximum page size that it returns for any given request.” from http://technet.microsoft.com/en-us/library/aa997429(EXCHG.80).aspx and you will get a warning from bpa when the number is bigger than 900.
this is so cool. because what I have seen the lagest organization only have 176 servers.