What is a Property Set?
Basically it is a grouping of Active Directory Objects in this case related to Exchange for use in day to day operations.
How have they changed in Exchange 2007?
The legacy equivalent of the property sets within Exchange 2007 were simply addressed as Public Information within the directory. The primary ones were things such as
ms-Exch-ADC-Global-Names
ms-Exch-Alt-Recipient
In Exchange 2oo7 these are renamed as Exchange Property Sets and are much the same in terms of function.
The introduction of a new property set type in E2k7 called “Exchange Personal-Information” was done specifically to address security issues with respect to the directory. When used, the attribute is only accessible to the Owner of the object and the Administrators and removes the possibility that Authenticated users can access personal data through the read-only access granted by default in previous versions of the product.
A good example of an attribute which uses the new property set is the “ms-Exch-UM-PIN-Checksum ” which controls the PIN for access to Unified Messaging features such as OVA or similar.