We recently upgraded all our Exchange 2010 infrastructure to SP1 without a single hurdle.
The Servers were upgraded in the order Cas-hub1, Cas-hub2, Dagnode1, Dagnode2.
We had the hotfixes (64bit) for windows server 2008 R2 downloaded along with the latest FilterPack.
I started by installing the FilterPack on each Server and then running the Setup wizard which checks for prerequisites. A restart was performed after every step just for my comfort. Finally the Setup allowed me to install the Exchange 2010 after all prereqs were met. I preferred this method rather than doing every step on my own, the Exchange 2010 SP1 setup is intelligent enough to tell you what it wants. I had configured HTTPS redirection on my default website so after the SP1 install I had to uncheck "Require SSL" on my Default Website. This brought my OWA back to life.
We use thirdparty Certificates for Exchange, so I had no issues with my Certificate. No issues with EMC too.
As we use UAG, the external OWA display was not functioning. So we had to add 4 new rules to UAG and the steps are outlined in Technet. I also recommend to install TMG SP1 + Update 1 for SP1 on UAG as it has support for Exchange 2010 SP1. If you use TMG for publishing do the upgrade on TMG.
I also had to modify the RCA related parameter in the Default Throttling Policy to null so as to ensure that my BES server functions properly and no blackberry handheld was affected. The BES Server was restarted after the entire upgrade process was over.
After the upgrade process was completed on all the Servers, I realised that Microsoft has released RollUp Update 1 for Exchange 2010 SP1 on Oct 8 which sorts out certain key issues, though I didn't have any.
But to be safe I installed that too on all the servers.
I believe Exchange 2010 SP1 has major issues when installing or upgrading in a virtualised environment especially if the VMs are not as per MS best practices. Luckily we have not created a virtual environment for Exchange as yet. May be this saved us.
Guys, SP1 Rocks...Microsoft has done a good job...Now its time to do some marketing for all these new features to our employees.