If you get the following error message when running the upgrade assistant to migrate from OBIEE 10g to 11g:
[2012-10-15T09:52:07.080+02:00] [Framework] [ERROR]  [upgrade.Framework] [tid: 14] [ecid: 0000JdZQ8_c5aal6wvaeMG1GUw1s000005,0] UPGCMP-02712: Expected oracle.biee.admin:oracleInstance=*, type=BIDomain.BIInstanceDeployment.BIComponent,biInstance=*, process=*_obips1, group=Service Oracle instance, found 0
Then you have to check your topology.xml file. You can find it at <FMW_HOME>/user_project/domains/bifoundation_domain/opmn/. Check if the host attribute within tag <ias-instance> links to your current BI hostname. This was not in my case.
If you get the error that more then 1 instance is found check this file also. The upgrade assistant only supports 1 instance. This is summarized at Oracle Nerd.