Just did the APM 2.0 install - important tip...don't run the upgrade directly from within a remote desktop connection.. as the release notes say:
If you are installing Application Performance Monitor through a terminal server session, use the Add or Remove Programs utility on you server (Start > Control Panel > Add or Remove Programs) to run the Application Performance Monitor installer.
In this case, I can confirm (blush) that NOT RTFM-ing that part of the release notes gave me considerable grief.. the install appeared to go find, but when you went to access Orion you'd get a APM cannot connect to engine error message.
Otherwise, it went fine!!
Don