I received mine today. It says like Firewater said that it is only a trial until Nov. But Apple doesn't usually offer trial versions of their software do they? I would think this is the full version and it won't actually turn off in Nov, but I could be wrong. I wouldn't risk my server going dead on Nov 30.
Yes, Apple does offer trials. iWork is an example.
In the case of Mac OS X Server, unlike client, it uses a serial number. The serial you received is only good til Nov. 30. After which, you will need to enter a purchased serial. You will not be able to do anything after that date without entering the serial from a purchased copy.
So, the OS you are receiving is the full version, but you can only use it til Nov. 30. Do you really think Apple would allow for such a loophole? "Request a trial and get the whole thing for free!" Really? Apple is just going to send you $500 software and let you use it indefinitely? Does that make any sense to you?