I give up, my installation is hosed and I'm crippled.
I tried running the 1.5 sql template, substituting all the variables for their default values. When I try to access OpenGoo I get:
We are sorry, but OpenGoo is not currently able to execute your request. An Error Report has been sent to the administrator.
I have successfully reverted to 1.4.2 though, simply by restoring the db backup I made prior to upgrading, and uploading the 1.4.2 files.