The whole universe knows by now that RU5 for Exchange 2007 SP1 has hit the streets.
You can download it here: http://www.microsoft.com/downloads/details.aspx?FamilyID=652ed33a-11a1-459c-8ffe-90b9cbfe7903&DisplayLang=en
Ninob over at the Exchange team blog says that it will be out via Microsoft Update in the next few weeks. He also mentions another good point, that is you want RU5 to install in minutes and NOT HOURS check out 944752: Exchange Server 2007 managed code services do not start after you install an update rollup for Exchange Server 2007. Check out my post on a script that will do this for you. However RU5 will do the update too
You can check the KB out here: 953467: Description of Update Rollup 5 for Exchange Server 2007 Service Pack 1. Revision 1.1 lists 48, yeah thats right 48 fixes!
This looks good : 949722 – Event ID 800 does not include the user name of users who ran the Get-MessageTrackingLog command in an Exchange 2007 environment <http://support.microsoft.com/kb/949722/>