or those that subscribe to the Public Internet Connector (PIC) feature in Office Communication Server, a recent change at AOL may impact you. As with all communication to and from OCS, certificates are used to encrypt and authenticate traffic. The PKI infrastructure AOL utilized in the past has changed and they have moved to their new AOL root certificates. Because of this, the OCS Edge/Access Proxy servers will not be able to validate any AOL traffic without a root certificate update.
The official notice may be found here:http://blogs.msdn.com/scottos/archive/2008/12/02/office-communicator-clients-cannot-communicate-with-contacts-homed-on-aol.aspx
A link to the AOL certificates may be found directly here: https://pki-info.aol.com/AOL/
Remember. only the edge servers (those authenticating traffic) require the updates - not your clients - and a restart/reboot is not required
Exchange 2007 RU5 was released yesterday approximately 6 weeks after RU4 was released. The current release corrects numerous bugs with the complete list found athttp://support.microsoft.com/kb/941421. The roll-up does not require a reboot but may take a considerable amount of time to install so be prepared. In testing I have not encountered any issues installing the roll-up and unlike RU4 all services did start as expected. Expect to see the RU released via Microsoft Update the first half of December. Until then, you can download the update directly from Microsoft Download at http://www.microsoft.com/downloads/details.aspx?familyid=652ed33a-11a1-459c-8ffe-90b9cbfe7903&displaylang=en&tm.