I visited a customer recently who was running Exchange Server 2007 but could not tell me which service pack was installed.  Not a problem, its just a quick powershell command to find out.

[PS] C:\>Get-ExchangeServer | fl name, *version*

Name                : EX2007
AdminDisplayVersion : Version 8.2 (Build 176.2)
ExchangeVersion     : 0.1 (8.0.535.0)

The AdminDisplayVersion attribute is the one to look at.

You can look up the complete list of Exchange version numbers here.