I am also having a problem with Update 1. Same problem as Gerard.
I get a warning about flogon.js. After doing some troubleshooting, it looks like Update 1 didn't copy all of the OWA files. If i go to this directory:
D:Program FilesMicrosoftExchange ServerV14ClientAccessOwa14.0.682.1scriptspremium
The only file in there is uglobal.js. flogon.js (and all of the other files that should be are gone).
This is a clean install on Windows 2008 R2. Installed OS, installed Exchange 2010, installed Update 1.
I uninstalled Update 1 and the files came back. I reinstalled Update 1 and the files stayed there, but i still couldn't logon to OWA. It complained about an error in auth/logon.aspx. I enable anonymous authentication on the directory, tried OWA, it gave a error that OWA could not start which is normal with anonymous is checked. Next I unchecked anonymous and tried again and OWA was up.
Strange...