We are currently user testing 32-bit Notes Standard v8.5.3 FP1 under Citrix XenApp 6.5 (on 64-bit Windows Server 2008 RC2) and ran into a weird problem with the embedded Sametime 8.5.2 client . . .
When you clicked on "Log In" in the Sametime ('ST') client in the Notes Sidebar, the ST login dialog would open, but was unresponsive for 20-30 seconds, then work fine.
Similarly, if you then enter login credentials, remember password, the next time you logged into ST, Notes would 'hang' (be unresponsive) for 20-30 seconds. Or, if you selected to auto login to ST, whenever you started Notes 8.5.3, it would 'hang' for 20-30 seconds, then work fine.
1. Windows Explorer to "C:\Program Files (x86)\IBM\Lotus\Notes\framework\rcp".
2. Edit the "plugin_customization.ini" file with Wordpad.
3. Change the setting "com.ibm.collaboration.realtime/startBroker=" from "true" to "false".
Many thanks to Christian Henseler for suggesting the above technote, which contained the solution.